Fix URL related escaping for oauth2

[wxiaoguang]

Follow up #37327. See the comments.

• Root problem: the design of OAuth2 providers is a mess, the display name is used as provider's name and used in the URL directly
• The regressions:
  • When trying to fix OAuth2 Authentication Service Redirect URL Does Not Encode Apostrophes #36409 , it introduced inconsistent URL escaping for the "path" part.
• This fix: always use "path escaping" for the path part, add more tests to cover all escaping cases.

Now, frontend "pathEscape" and "pathEscapeSegments" generate exactly the same result as backend.

[Copilot]

Pull request overview

This PR fixes inconsistent URL escaping for OAuth2 auth source names when used as URL path segments, aligning frontend, templates, and backend routing/lookup behavior and adding tests to cover special-character cases.

Changes:

• Switch OAuth2 provider links/callback URL generation from query-escaping to path-escaping (spaces %20, consistent handling of +, ', etc.).
• Add/adjust frontend and backend tests to lock in escaping behavior for query vs path components.
• Treat “OAuth2 source not found” as a not-exist error so it can be handled as a 404 instead of a 500.

Reviewed changes

Copilot reviewed 16 out of 16 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
web_src/js/utils/url.ts	Adds urlQueryEscape and pathEscape, and updates pathEscapeSegments to match backend escaping semantics.
web_src/js/utils/url.test.ts	Adds unit tests for query/path escaping and segment escaping cases (space/plus).
web_src/js/utils.ts	Removes urlQueryEscape from the generic utils module (relocated to utils/url.ts).
web_src/js/utils.test.ts	Removes urlQueryEscape test/import now that function moved.
web_src/js/features/admin/common.ts	Uses path escaping when showing the OAuth2 callback URL on the admin auth source page.
tests/integration/oauth_test.go	Expands integration coverage for OAuth source names with spaces/plus and verifies rendered login links.
templates/user/settings/security/accountlinks.tmpl	Path-escapes OAuth2 source names when generating account-link URLs.
templates/user/auth/external_auth_methods.tmpl	Path-escapes OAuth2 provider display names in login links.
services/context/context_response.go	Adds ErrNotExist→404 handling in ServerError and changes 404 plaintext body behavior.
services/context/base_path.go	Adds SetPathParamRaw for pre-escaped route params (primarily useful for tests).
routers/web/auth/oauth.go	Decodes provider using PathParam (path-unescape) rather than query-unescape.
routers/web/auth/auth_test.go	Updates OAuth2 auth tests for special characters and raw path-param setting.
routers/web/auth/auth.go	Uses url.PathEscape for OAuth2 provider path generation during auto-redirect.
modules/util/util_test.go	Adds a backend test for PathEscapeSegments behavior (space/plus).
modules/templates/helper_test.go	Adds reference tests for Go’s QueryEscape vs PathEscape outputs.
models/auth/oauth2.go	Returns util.NewNotExistErrorf when an OAuth2 source name isn’t found.

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[wxiaoguang]

Should be 100% correct now.

[silverwind]

And btw sorry for the invalid reviews from GPT-5.4. This was an experiment. It took like 10 times as long as Claude would and produced shitty results, so I will be more careful reviewing with that model in the future.