feat(rendering): slice 9 — ghost plane in the ledger pass + sidecar-tail e2e

[Juliusolsson05]

Stage 1, slice 9. The five-rule ghost predicate (#428) existed standalone — the ledger never consulted it. This wires the ghost plane end-to-end:

• `LedgerInput` gains an optional `ghosts` plane (`GhostLedgerCandidate` = paintable candidate + predicate facts) and `ghostContext` (rules 3/4). Optional because most sessions never mint a ghost and opencode's supersede-less ghosts get gated out in the adapter, before the ledger.
• Ghosts are decided last — lowest-trust source, they only fill gaps the authoritative planes left; survivors compete in ordering via the existing `ghost-fallback` SOURCE_RANK.
• Identity-stability cache (D11) compares `ghostContext` field-wise (scalar tail + set reference), so adapters can mint the context object fresh each tick.
• New e2e fixture `fixtures.sidecarTailGhost.test.ts` pins the dominant production trap: sidecar blurb and stuck tool_use ghost both pass rules 1–4; only the shape backstop separates them. Plus committed-catch-up kill and cache-identity-with-fresh-context tests.

Closes the "sidecar-tail e2e variant" item from the Stage 1 progress marker. 53/53 pipeline tests; tsc gate (node + web) clean on main + integration diff.

🤖 Generated with Claude Code