docs: rename /docs to /user-docs for consistency

Rename the user documentation URL path from /docs to /user-docs to match
the naming convention of /admin-docs and /developer-docs.

Changes:
- Add routeBasePath: 'user-docs' to preset-classic docs config
- Add createRedirects for /docs/* → /user-docs/* pattern-based redirects
- Update all redirect destinations from /docs/* to /user-docs/*
- Update navbar links to use /user-docs/
- Update sitemap priorities to use /user-docs/
- Update internal links in user docs, admin docs, and developer docs
- Update footer security link to /admin-docs/security/

All old /docs/* URLs will automatically redirect to /user-docs/* via
the createRedirects function. Versioned docs at /docs/6.0.0/* remain
unchanged.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docs/developer_docs/contributing/development-setup.md

@@ -653,7 +653,7 @@ export enum FeatureFlag {
 those specified under FEATURE_FLAGS in `superset_config.py`. For example, `DEFAULT_FEATURE_FLAGS = { 'FOO': True, 'BAR': False }` in `superset/config.py` and `FEATURE_FLAGS = { 'BAR': True, 'BAZ': True }` in `superset_config.py` will result
 in combined feature flags of `{ 'FOO': True, 'BAR': True, 'BAZ': True }`.
 
-The current status of the usability of each flag (stable vs testing, etc) can be found in the [Feature Flags](/docs/configuration/feature-flags) documentation.
+The current status of the usability of each flag (stable vs testing, etc) can be found in the [Feature Flags](/admin-docs/configuration/feature-flags) documentation.
 
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