Slice 1: scaffolding + propose-to-super-draft vertical

Brings the §1 bot wrapper, the §4 cache (webhook + reconciler), the
§5 schema (six numbered migrations), Gitea OAuth + §6 user
provisioning, the §7 catalog left pane, and the propose-to-merge
vertical: propose modal opens an idea PR against the meta repo, an
owner merges from the pending-idea view, the cache picks it up via
webhook or reconciler sweep, and the catalog renders the new
super-draft.

Per §1 the bot is the only Git writer; every commit, branch
creation, and PR merge carries the §6.5 On-behalf-of: trailer and
an `actions` audit row. Per §4 the cache is never written from a
user action — it's webhook+reconciler only.

Covered by `backend/tests/test_propose_vertical.py` against an
in-process Gitea simulator.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend/migrations/002_cache.sql

@@ -0,0 +1,82 @@
+-- §4: the metadata cache. Reconstructible from Gitea at any time by the
+-- §4.1 reconciler; never written from user actions, only from webhook
+-- handlers and reconciler sweeps. Body content is cached for main-branch
+-- reads (§4 #3); branch bodies are not.
+--
+-- These tables are not in §5's "canonical app tables" list because they
+-- are cache, not truth — but they are required for the left-pane render
+-- path and for serving super-draft and main-branch bodies without a
+-- Gitea round-trip on every navigation.
+
+-- One row per meta-repo rfcs/<slug>.md entry. Mirrors §2.1 frontmatter
+-- plus the cached body for super-draft preview (graduated entries have
+-- frontmatter-only bodies per §13.3 step 3, but the field is reused).
+CREATE TABLE cached_rfcs (
+    slug                TEXT PRIMARY KEY,
+    title               TEXT NOT NULL,
+    state               TEXT NOT NULL CHECK (state IN ('super-draft', 'active', 'withdrawn')),
+    rfc_id              TEXT,                -- 'RFC-NNNN' or NULL until graduated
+    repo                TEXT,                -- 'org/repo' or NULL until graduated
+    proposed_by         TEXT,                -- gitea login or email
+    proposed_at         TEXT,
+    graduated_at        TEXT,
+    graduated_by        TEXT,
+    owners_json         TEXT NOT NULL DEFAULT '[]',
+    arbiters_json       TEXT NOT NULL DEFAULT '[]',
+    tags_json           TEXT NOT NULL DEFAULT '[]',
+    body                TEXT,                -- super-draft body or main RFC.md body
+    body_sha            TEXT,                -- the commit sha the body was fetched at
+    last_main_commit_at TEXT,                -- §7.1's "Recently active" sort
+    last_entry_commit_at TEXT,               -- last meta-repo commit touching this entry
+    updated_at          TEXT NOT NULL DEFAULT (datetime('now'))
+);
+
+CREATE INDEX idx_cached_rfcs_state ON cached_rfcs (state);
+CREATE INDEX idx_cached_rfcs_last_active ON cached_rfcs (
+    COALESCE(last_main_commit_at, last_entry_commit_at) DESC
+);
+
+-- One row per branch the bot knows about on either a per-RFC repo
+-- (rfc_slug, state='active'') or on the meta repo as a super-draft edit
+-- branch (rfc_slug, state='super-draft', branch_name like 'edit/<slug>/...').
+-- §11.5: closed branches stay; deleted branches keep their metadata row
+-- per §12 ("branch removed from Gitea, row remains").
+CREATE TABLE cached_branches (
+    id              INTEGER PRIMARY KEY AUTOINCREMENT,
+    rfc_slug        TEXT NOT NULL,
+    branch_name     TEXT NOT NULL,
+    head_sha        TEXT,
+    state           TEXT NOT NULL DEFAULT 'open' CHECK (state IN ('open', 'closed', 'deleted')),
+    pinned          INTEGER NOT NULL DEFAULT 0,
+    created_at      TEXT NOT NULL DEFAULT (datetime('now')),
+    last_commit_at  TEXT,
+    closed_at       TEXT,
+    UNIQUE (rfc_slug, branch_name)
+);
+
+CREATE INDEX idx_cached_branches_rfc ON cached_branches (rfc_slug, state);
+
+-- One row per PR the bot knows about. Includes meta-repo idea PRs (rfc_slug
+-- carries the proposed slug, see §5 super-draft scoping note) and meta-repo
+-- body-edit PRs and per-RFC-repo PRs. The pr_kind disambiguates.
+CREATE TABLE cached_prs (
+    id              INTEGER PRIMARY KEY AUTOINCREMENT,
+    rfc_slug        TEXT NOT NULL,
+    pr_kind         TEXT NOT NULL CHECK (pr_kind IN ('idea', 'meta_body_edit', 'meta_metadata', 'meta_claim', 'rfc_branch')),
+    repo            TEXT NOT NULL,                -- 'org/repo' the PR lives on
+    pr_number       INTEGER NOT NULL,
+    title           TEXT NOT NULL,
+    description     TEXT,
+    state           TEXT NOT NULL CHECK (state IN ('open', 'merged', 'closed', 'withdrawn')),
+    opened_by       TEXT,                          -- gitea login (resolved from On-behalf-of trailer where present)
+    opened_at       TEXT,
+    merged_at       TEXT,
+    closed_at       TEXT,
+    head_branch     TEXT,
+    base_branch     TEXT NOT NULL DEFAULT 'main',
+    head_sha        TEXT,
+    UNIQUE (repo, pr_number)
+);
+
+CREATE INDEX idx_cached_prs_rfc ON cached_prs (rfc_slug, state);
+CREATE INDEX idx_cached_prs_kind ON cached_prs (pr_kind, state);