(session-state): local-pty rows carry a persistent state like the other adapters

[devsuitup]

Finishes #246 (steps 1-5 shipped in #266–#270; #273 added the ownership rule). This closes the last gap: the local-pty kind now holds a persistent createSessionState per session like remote-ssh and local-transcript, instead of projecting from the legacy Maps at render time.

What

• public/session-activity.js is the local-pty adapter: localPtyStates (one state per id) fed by setActivity, clearUnread, new setAttention(sessionId, on, via), syncLocalPtyAgentsBusy (aggregate of activeSubagentsByParent), rekeyActivityState, purgeActivityFor. Exported signatures unchanged. sessionBusyState / responseReadySessions / attentionSessions remain as Map/Set-shaped views over the states for the two readers not migrated (sidebar initial paint, grid-card dot) and for tests.
• public/session-activity-dom.js: applyStateClasses(sessionId, snapshot) is the single projection for all three kinds and now writes needs-attention too; computeBusyReadyClasses / applyActivityClassesToElement removed; snapshotForLocal is a thin wrapper.
• app.js: notifications go through setAttention; sidebar.js: subagent running state mirrored into the adapter.
• Exclusivity of busy / response-ready / attention now lives only in session-state.js apply().
• Decided semantic, documented and pinned: an attention event consumes the unseen-response state — clearing attention lands on idle, not on response-ready (before: independent Sets, CSS precedence, fallback to response-ready).
• Docs: session-state.md (status complete, local-pty section, ports table corrected), ipc-bridge.md.

Proof

• DOM output unchanged except the two decided semantics (attention orthogonal to busy; local idle-while-active reads "Waiting for input") — see the review comment; the full pinning suite is green (dom-sidebar-icon-slot, sidebar-busy-agents-tint, session-icon-slot-css-boundary, dom-sidebar-subagent-running, remote-row-ownership, remote-session-adapter, local-transcript-adapter, activity-trace-renderer, running-indicators, dom-file-panel-changes).
• test/local-pty-adapter.test.js (12): sequence → snapshot, combined states impossible through the API, rekey/purge move/drop the object, the decided attention semantic, a mutation guard.
• Mutation: setActivity writing sessionBusyState.set() directly instead of apply() → 3 tests red; reverted.
• Three tests in session-activity.test.js that forced now-impossible combinations were rewritten to cover the same regressions without them.
• task check: 1431 + 120 pass, 0 fail, pre-existing skips.

Left as is: activeSubagentsByParent (per-agent TTL tracking) is a different concern; its aggregate is mirrored, not replaced.

[devsuitup]

Adversarial review (main vs branch in jsdom) → second commit. "DOM output unchanged" in the body reads: unchanged except two decided semantics.

1. MAJOR — an OSC-0 busy title while a permission prompt is open wiped needs-attention. Fixed in the domain: clearExclusive() no longer touches attention; a busy edge leaves it, only an explicit clear removes it. The projection now reads busy / attention / response-ready off the snapshot rather than the winning rung, so both classes show together as on main. Tests: attention → busy → both classes; clear attention → busy remains. Mutation: restoring attention = false in clearExclusive() → 3 tests red.
2. MAJOR — a local row idling while active (or via an armReady:false source) now reads "Waiting for input" instead of "Idle". Kept as a convergence with remote and local-transcript rows; documented under "Decided" and pinned by two tests (active → session-icon--waiting; not active → response-ready, unchanged).
3. MINOR — docs/activity-trace.md: needs-attention is a field of class.apply now; class.toggle only carries has-running-pty. One assertion added.
4. MINOR — syncLocalPtyAgentsBusy no longer creates a state; setRemoteAttached(id,false) purges the shadow local-pty entry (remote-detach). Two tests.

task check: 1440 + 120 pass, 0 fail.