feat: split local/remote config and add projects drawer

[flexdinesh]

• Behavior owner and resulting change:
  • config: CLI config is namespaced into local.* (diffx [PATH]) and remote.* (sync/hooks), with DIFFX_LOCAL_* / DIFFX_REMOTE_* env. diffx-server reads only DIFFX_SERVER_* and defaults to port 7980, so it runs beside local 7981–7990. Flat config files are rejected with an error naming the file and each key's replacement.
  • cmd/diffx: new diffx remote status checks the destination, credential, and protocol, and lists waiting hook deliveries. Hooks check remote config before discovery.
  • hooks: automatic retries skip jobs whose worker ran in the last 2 minutes; collector retry still forces them.
  • reviewstore / contextservice / httpapi: contexts expose streamId and latestContextId. /api/v2/contexts?latest=true omits stale snapshots.
  • apps/web: collapsible Projects drawer listing repositories with their current changed streams, plus a new-changes dot and a "View latest" notice. Stream heads load continuously; the picker loads full history only while open.
• Contracts/invariants affected; local/remote implications:
  • Breaking: old flat config is rejected. The CLI and server must be upgraded together.
  • Compose publishes on DIFFX_SERVER_PORT (default 7980).
  • The viewed review is never swapped on ingestion.
  • Unconfigured hooks no longer enroll identities in .git.
• Validation results; remaining risks:
  • mise run check and the pre-push check:push pass: Go, race, conformance, contracts, design guard, 65 browser tests including a new drawer test, and unit tests.
  • Manually verified against a real diffx-server fed by diffx sync: desktop, collapsed, dark, and mobile drawer focus/Escape.
  • Risk: the browser-test fixture reads personal config, so local checks fail until a dev's flat config is migrated or deleted.
• Intentional architecture/design changes and rationale (if any):
  • Mode is chosen by the command, not by a config field; namespaces keep the modes from reading each other's settings.
  • New --projects-width token and a new-changes status-circle design exception, both documented in DESIGN.md.
  • The file-sidebar toggle uses a list-tree icon so the two panel toggles stay distinct.
• UI evidence: affected themes/layouts, keyboard use, Pierre geometry (if applicable):
  • Light/dark, desktop expanded/collapsed, and modal drawer below 1012px.
  • Drawer focus moves in on open and Escape restores it to the toggle.
  • Pierre geometry is unchanged; the diff only loses the drawer's width.