feat: deliver personal center usage analytics

[knqiufan]

Summary

• deliver the complete P0-P8 personal center and usage analytics plan
• add local profile editing and managed avatars, usage overview, 365-day activity calendar, and 30-day model trend
• unify Rig/MCP/Sidecar usage capture into an append-only SQLite ledger with exact/estimated/legacy/unknown quality semantics
• add idempotent finalize, lifecycle/import-export behavior, lazy rebuildable rollups, and Schema v16 repair for installations that reached v15 before rollup tables existed
• synchronize architecture, implementation, UI, project-structure, and development-status documentation

Data and migration safety

• Schema v15 owns user_profiles and llm_usage_events as durable facts
• Schema v16 only creates/recreates disposable usage rollup tables
• upgrades create misaka.pre-v16.sqlite3 before migration
• the migration regression test reproduces a v15 database with ledger rows but missing rollups, then verifies preservation, dashboard rebuild, idempotency, and backup restoration

Verification

• cargo test --all-features -j1: 511 tests passed
• cargo test --all-features --test db_migrations_tests -j1: 22 passed
• cargo check --all-features
• cargo fmt --all --check
• npm test: 50 files / 313 tests passed
• npm run build
• Sidecar delivery gate: 41 pytest tests passed
• 100k usage-event hot dashboard P95: 64.8ms

cargo nextest run --all-features --profile ci was attempted locally during P8, but Windows ended rustc with OS 1455 (paging-file resource limit). The repository-documented serial fallback completed successfully; no cargo clean was used.