docs(adr-022): mark Accepted, update env/compose/migration docs for LOGIN_FLOW rename

Follow-up to the LOGIN_FLOW rename. The user-facing surface area —
env.sample, docker-compose.yml mcp-login-flow profile, migration
guide, ADR statuses, and the running.md boot-log examples — all need
to refer to `login_flow` rather than the deprecated
`oauth_single_audience` string.

- docker-compose.yml: add explicit MCP_DEPLOYMENT_MODE=login_flow to
  the mcp-login-flow profile (no longer relying on auto-detection).
- env.sample: update the deployment-mode list and example, dropping
  the removed `oauth_token_exchange` and pointing at ADR-022 for the
  rename rationale.
- docs/ADR-022: flip Status to Accepted with a note that this PR
  implements step 1 (rename + validation gate).
- docs/ADR-021: note that it has been partly superseded by ADR-022
  (the oauth_single_audience naming is no longer accurate); cross-link.
- docs/ADR-025: drop oauth_single_audience/keycloak from the dynaconf
  validator example and the [oauth_single_audience] TOML section.
- docs/configuration-migration-v2.md: bulk-replace oauth_single_audience
  → login_flow throughout (sed -i).
- docs/running.md: re-collapse the per-mode boot-log subsections (added
  during the closed PR #786 workaround) back into a uniform
  "<mode>"-substitution block — now correct after this PR's logging
  cleanup at app.py:1172.

No code changes in this commit.

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

docs/running.md

@@ -336,29 +336,19 @@ messages in the container logs:
 **At server boot (all modes):**
 ```
 INFO     ✅ Configuration validated successfully for <mode> mode
+INFO     Configuring MCP server for <mode> mode
 INFO     Health check endpoints enabled: /health/live, /health/ready
 ```
 
-`<mode>` is one of `single_user_basic`, `multi_user_basic`, or
-`oauth_single`, matching the `MCP_DEPLOYMENT_MODE` setting.
-
-**Additional BasicAuth-mode messages (at server boot):**
-```
-INFO     Configuring MCP server for <mode> mode
-```
-
-Here `<mode>` is the enum value (`single_user_basic` or `multi_user_basic`).
+`<mode>` is one of `single_user_basic`, `multi_user_basic`, or `login_flow`,
+matching the `MCP_DEPLOYMENT_MODE` setting.
 
 **Additional OAuth-mode messages (at server boot):**
 ```
-INFO     Configuring MCP server for OAuth mode
 INFO     OAuth client ready: <client-id>...
 INFO     OAuth configuration complete
 ```
 
-Note the OAuth boot line logs the literal string `OAuth mode`, not the enum
-value `oauth_single`.
-
 **Additional single-user BasicAuth messages (per MCP session):**
 
 These fire when the first MCP client connects, not at server boot — if you