feat(steam): compose Wake context from Timer state

[kachofugetsu09]

Summary

• physically remove PROACTIVE_COMPONENTS, ProactiveSourceSpec, and proactive-only get/take MCP tools
• make an ordinary Core Timer the single Steam polling owner and share one steam_runtime domain library with user-driven MCP queries
• store presence as overwriteable current state while retaining all meaningful snapshot and snapshot-run history
• append only fresh channel=wake context; passive, stale, and unknown state have no prompt effect
• derive transitions from durable previous state rather than process-global memory
• rotate MCP and context diagnostics at 5 MiB with three retained generations

Migration and ownership

The existing steam_proactive.sqlite3 filename is retained only to inherit formal history in place; no proactive runtime capability remains. Existing formal evidence contains 157 snapshot runs and 365 snapshots. Initialization first validates the complete legacy schema read-only, then performs compatible DDL, indexes, and backfill in one explicit transaction. Incompatible or interrupted migration leaves bytes, schema, rows, and sidecars unchanged.

Validation

• 25 tests passed against Core 9da3a988a2bf62b0f550bd4f6bb98c4eeb1f56f5
• real Manager + stdio MCP + Timer + Wake/passive fixtures passed
• candidate fixture proves isolated MCP handshake with zero Timer, formal writes, or Steam network calls
• reload fixture proves old Timer cancellation and cleanup before one new Timer remains
• Pyright: 0 errors and 0 warnings
• exact Plugin API v3 contract, compileall, and git diff --check passed
• exact migration head 4ba37db received independent Terra xhigh APPROVE

The only test warning is the existing FastMCP/Pydantic lifespan forward-reference warning.

Recovery

Pre-change bundle: /mnt/data/coding/backups/steam-context-v3-20260823/pre-implementation-337c8f1.bundle
Pre-migration-fix bundle: /mnt/data/coding/backups/steam-context-v3-20260823/pre-terra-fix-0be2843.bundle

This PR does not deploy or change the formal hua-home workspace.