docs: backfill CLI website docs

[marcus]

Summary

• Add focused Docusaurus pages for notes, sync and collaboration, configuration, and troubleshooting.
• Refresh the command reference/sidebar so implemented CLI commands are discoverable.
• Align review-policy documentation with current main: delegated mode is the default, with balanced documented only as legacy compatibility.

Verification

• npm ci (website)
• npm run build (website)
• go test github.com/marcus/td
  github.com/marcus/td/cmd
  github.com/marcus/td/cmd/td-sync
  github.com/marcus/td/internal/agent
  github.com/marcus/td/internal/api
  github.com/marcus/td/internal/config
  github.com/marcus/td/internal/crypto
  github.com/marcus/td/internal/dateparse
  github.com/marcus/td/internal/db
  github.com/marcus/td/internal/dependency
  github.com/marcus/td/internal/events
  github.com/marcus/td/internal/features
  github.com/marcus/td/internal/git
  github.com/marcus/td/internal/input
  github.com/marcus/td/internal/models
  github.com/marcus/td/internal/output
  github.com/marcus/td/internal/query
  github.com/marcus/td/internal/reviewpolicy
  github.com/marcus/td/internal/serve
  github.com/marcus/td/internal/serverdb
  github.com/marcus/td/internal/session
  github.com/marcus/td/internal/suggest
  github.com/marcus/td/internal/sync
  github.com/marcus/td/internal/syncclient
  github.com/marcus/td/internal/syncconfig
  github.com/marcus/td/internal/version
  github.com/marcus/td/internal/workdir
  github.com/marcus/td/internal/workflow
  github.com/marcus/td/pkg/monitor
  github.com/marcus/td/pkg/monitor/keymap
  github.com/marcus/td/pkg/monitor/modal
  github.com/marcus/td/pkg/monitor/mouse
  github.com/marcus/td/test/syncharness
• go test ./test/e2e -run '^(TestHarnessBasic|TestVerifyConvergence|TestVerifyActionLogConvergence|TestVerifyMonotonicSequence|TestVerifyCausalOrdering|TestVerifyIdempotency|TestVerifyEventCounts|TestVerifyFieldLevelMerge|TestVerifyReadYourWrites|TestVerifyAll|TestServerRestart|TestEngine|TestEngineWeightedSelection|TestHistoryRecord|TestHistoryFilter|TestHistorySummary|TestHistoryWriteJSON|TestHistoryWriteReport|TestHistoryConcurrency|TestHistoryEmptySummary|TestRateLimitEnforced|TestPartitionRecovery|TestUndoSync|TestMultiFieldCollision|TestRapidCreateDelete|TestCascadeConflict|TestDependencyCycle|TestThunderingHerd|TestBurstNoSync|TestSmoke)$'
• go test ./test/e2e -run '^TestChaosSync$' -count=1 -chaos.actions=10

Note: full go test ./... was attempted twice and both runs failed only in randomized TestChaosSync convergence with time-based seeds; this docs-only branch does not touch Go code.