docs: address remaining Login Flow v2 review feedback

Round-2 cleanup of PR #743 review comments not covered by d153e96:

- configuration.md: fix broken `#multi-user-oauth-modes` anchor; replace
  with the two real anchors (Multi-User BasicAuth, Login Flow v2). Rewrite
  the stale "always use OAuth2/OIDC with pre-configured clients" Best
  Practices section to reflect the post-pivot mode matrix, and update the
  Docker volume example to mount the encrypted app-password store
  (`TOKEN_STORAGE_DB`) rather than obsolete `.oauth` client storage.
- semantic-search-architecture.md: rename remaining body references from
  the deprecated `VECTOR_SYNC_ENABLED` to `ENABLE_SEMANTIC_SEARCH` so the
  doc matches configuration.md / troubleshooting.md.
- running.md: relabel "OAuth Mode (Recommended)" as
  "Login Flow v2 / OAuth issuer mode (--oauth)", drop the misleading
  "(Legacy)" suffix from BasicAuth, drop the
  `NEXTCLOUD_OIDC_CLIENT_ID/SECRET` example (tied to the retired
  direct-OAuth-to-Nextcloud flow), and add a note explaining what
  `--oauth` actually enables post-pivot.
- keycloak-multi-client-validation.md, oauth-impersonation-findings.md:
  add a deprecation banner pointing at ADR-022 / Login Flow v2. Files
  retained because ADR-002 and CLAUDE.md still cite them.
- auth-flows.md: clarify under the Astrolabe → MCP diagram that the
  Nextcloud-OIDC JWKS path applies to Multi-User BasicAuth; under
  Login Flow v2 the MCP server validates tokens against its own JWKS.
- login-flow-v2.md: clarify the sticky-session note — affinity must key
  on the OAuth bearer token (or user-bound cookie), not source IP, since
  MCP clients may not maintain stable IPs across the provisioning flow.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docs/auth-flows.md

@@ -126,6 +126,8 @@ Astrolabe                     MCP Server                   Nextcloud OIDC
 - Tokens are validated by the MCP server using Nextcloud OIDC JWKS
 - Authorization check: `token.sub == requested_resource_owner`
 
+> **Note:** The diagram and JWKS source above apply to **Multi-User BasicAuth**, where Nextcloud is the IdP. Under [Login Flow v2](#3-login-flow-v2) the MCP server is its own OAuth issuer and validates Bearer tokens against its **own** JWKS (or via local introspection of opaque tokens) — Nextcloud's JWKS is not involved on the MCP-client → MCP-server leg. See the Login Flow v2 section below.
+
 ---
 
 ### 3. Login Flow v2