Merge mantra into the chapter uploads branch

Thirty-eight commits had landed on mantra since this branch left it. Six
conflicts, all of them two sessions adding to the same place: the string
catalogue, the docs index, and the four files the projects line and this one
both touched.

Only one needed a decision. Both sides added parameters to
ProposedEvent.summarize -- chatRoomId and resolve for naming a project's owner,
chunkCount for saying how many chunks travel with a chapter -- so the signature
is the union, with chunkCount last so nothing positional on either side moved.
FrostSigningScreen and ProposalListViewModel pass all three, and the signing
screen's summary now names the thing, resolves its ids, and counts the batch.

The submodule pin is identical on both sides, and mantra's schema v20 to v22
does not collide: this branch adds no entity and no migration.

1170 tests, no failures; m3Audit's budgets all met.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

docs/README.md

@@ -9,6 +9,7 @@ silent, or a decision that looked arbitrary and was not.
 | [shared-key-ceremony.md](./shared-key-ceremony.md) | ChillDKG over NIP-17: the rounds, the approval gates, the chat transcript, participant ordering |
 | [shared-key-derivation.md](./shared-key-derivation.md) | deriving further keys from the group's threshold key with FROST tweaks — why not BIP32, why no chain code, and the one rule that must not be broken |
 | [subgroups.md](./subgroups.md) | a group making another group — the four ceremonies, what the parent's signature actually covers, and why the child's key is fresh rather than derived |
+| [subgroups-multiple-parents.md](./subgroups-multiple-parents.md) | adding a parent to a group that already exists — two signings and no ceremony, why the child's consent is the whole gate, and the certificate a group can truthfully sign about itself |
 | [frost-batch-signing.md](./frost-batch-signing.md) | signing several events in one ceremony — why one nonce can never cover two messages, and the phased schema, wire and UI work that follows from it |
 | [marmot-membership.md](./marmot-membership.md) | how members join an MLS group, and the epoch race that makes a missing member look like a successful invite |
 | [member-chronicle.md](./member-chronicle.md) | handing a member added after the work was done the group's signed record — why the events are not on the wire at all, and why the room's id is enough to verify them |
@@ -22,6 +23,7 @@ silent, or a decision that looked arbitrary and was not.
 | [jvm-target.md](./jvm-target.md) | what desktop support cost, phased — why the native chain was already done, why an empty source set in our phoenix fork was the real blocker, and why DAO tests need none of it |
 | [npub-profile-preview.md](./npub-profile-preview.md) | showing the person before a direct message is started from a pasted npub — why the preview is a screen keyed by public key, what "found" means when a row can be a placeholder, and the phase that makes the button honest about a key package that never comes |
 | [chapter-uploads.md](./chapter-uploads.md) | picking files off a device and having the group sign each one in as a chapter — why N files can never be one signing session, and the four things the single-chapter path gets away with |
+| [project-feature.md](./project-feature.md) | bringing the server schema's `project` and its two join models into a group that has no accounts and no server — a creator tag of its own and owners as a signed set of `p` tags, the role the parser has to be told about or every project lands ownerless, why a membership is its own signed event rather than a list, and the kind band that is already double-booked |
 | [material-design-conformance.md](./material-design-conformance.md) | what the M3 foundations actually require, measured against all 43 screens — the colour pairing that renders the app's own proposals invisible, and eight phases that put the decisions back in the theme |
 | [curated-to-mantra.md](./curated-to-mantra.md) | pulling the Curated fork's thirty-nine commits back under Mantra's names — which lines of work to take, the three decisions, and a measured way to replay a twice-rebranded history without touching seven hundred files by hand |
 | [curated-to-mantra-profiles.md](./curated-to-mantra-profiles.md) | the second pull: the fork's several-profiles line, ten commits and its first schema migration — which of it is a fix Mantra has today, who allocates a schema version number when two trees share one history, and the one conflict, which was Mantra's own |
@@ -39,7 +41,11 @@ and the one thing they cannot. The
 jvm-target note is unrelated to all of them: it is a build and packaging story.
 The subgroups note is a phased plan that has been built; it assumes both
 shared-key notes and reads as the ceremony's second half — what a group does
-once it has a key, and what it can say about a group that does not yet.
+once it has a key, and what it can say about a group that does not yet. The
+multiple-parents note is a phased plan that has been built, and reads only after
+it: it takes the one assumption that note never had to state — that a lineage is
+settled at founding — and finds that dropping it costs less than founding a
+subgroup does, because no ceremony is involved.
 The Material Design note is a phased plan that has not been built, and is the
 only one about what the app looks like rather than what it does; read the
 jvm-target note first if you want to know why its adaptive-layout phase exists.
@@ -82,3 +88,12 @@ built, because each of those is wrong in the single-chapter path today. Its two
 splitter phases are separable from the rest and worth reading on their own: what
 a chunk is, measured against the parser the web app translates with rather than
 assumed.
+The projects note is a phased plan that has been built as far as its seventh
+phase, and is the only one
+whose starting point is outside this repository: the platform's server schema,
+`mantra-db-models`, has had the three models for years. It reads as the
+translation domain's unanswered question — the app can say what a chapter is and
+who translated it, and cannot say what any of it is for — so read it after the
+nip30303 conventions are familiar, its decisions before its phases, and its scope
+fork before either, because that one changes the shape of the rest, and its
+table of where the build chose differently first.