feat: add CoreRoomSnapshot schema

[spytensor]

Linked Issue

Closes #242

Scope

Implemented:

• Added CoreRoomSnapshot as the v0.8 console data-plane contract.
• Included project identity, runtime/session/role state, public conversation visibility, WorkOrder rows, gates, evidence, sources, GitHub facts, health alerts, and layout hints.
• Added a realistic v0.8 fixture with blocked and stale work states.
• Added round-trip, validation, actionable-state, and unsupported-schema tests.

Not implemented:

• No ratatui renderer.
• No live GitHub polling.
• No mutating host actions.

Acceptance Criteria

• AC-1: Define a structured snapshot model for project identity, runtime, roles, conversation, work, gates, evidence, sources, GitHub state, alerts, and layout hints.
• AC-2: Project identity includes project, repository, remote, branch, head SHA, dirty state, version, active phase/milestone, and tracker issue.
• AC-3: Runtime snapshot includes host role, enabled roles, engine/model metadata, permission mode, session fresh/resumed state, active/inflight role, and waiting approval state.
• AC-4: Work snapshot preserves phase, epic, issue, branch, PR, CI, evidence, tracker, source citations, and lifecycle; it must not collapse to only title/state.
• AC-5: Schema round-trips through serde/TOML or JSON fixture.
• AC-6: Fixture covers a realistic CoreRoom project state with at least one blocked/stale item.

Changed Files

• src/console_snapshot.rs
• src/lib.rs
• tests/console_snapshot_test.rs
• tests/fixtures/console_snapshot_v08.toml

Validation

Local commands executed:

cargo fmt --all -- --check
cargo test --test console_snapshot_test --quiet
cargo clippy --all-targets --all-features -- -D warnings
cargo test --all-features --locked --quiet

Results:

• format: pass
• targeted console snapshot tests: pass, 3 tests
• clippy: pass
• full test suite: pass, ignored smoke tests unchanged

Evidence Packet

• WorkOrder: WO-0242
• GitHub issue: v0.8: Define CoreRoomSnapshot schema #242
• Gate thread: not applicable for this schema-only PR
• Evidence: schema/module + fixture + round-trip tests + full local validation above
• Not verified: GitHub CI until this PR runs checks

Tracker Update

• Tracker issue: v0.8.0 - CoreRoom Console Data Plane Tracker #238
• Updated checkbox: pending until merge
• Updated Milestone AC: M-AC-3 pending until merge
• Evidence Ledger row: will be updated after PR number/check status is available

Risk

Low. This adds a new schema module and fixture; no existing runtime path consumes it yet.

Rollback

Revert this PR. No state migration, package rename, or runtime behavior change is included.