fix(openwebui): parse bracketed IPv6 bind addresses - #6106

Description

OV_BIND=[::1]:18765 currently parses as host [ and port 8765, so the OpenWebUI tool-server entrypoint exits before serving. Parse bracketed IPv6 listeners before the existing hostname/IPv4 fallback so Uvicorn receives ::1 and the configured port.

Human Involvement

• A human participated in the implementation or review loop
• This PR was generated entirely by AI agents without human participation in the loop

Related Issue

Fixes #6105

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring (no functional changes)
• Performance improvement
• Test update

Changes Made

• Share bracket-aware host/port splitting between the two existing settings properties.
• Preserve hostname/IPv4 parsing and existing missing/invalid-port defaults.
• Add configuration regressions and document the IPv6 bind syntax. The original OpenWebUI integration is from feat(examples): add OpenWebUI tool-server plugin (#1387) #2640.

Testing

• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have tested this on the following platforms:
  • Linux
  • macOS
  • Windows

New configuration tests: the unmodified production base has 7 failures and 10 normal passes; the fixed complete OpenWebUI plugin suite has 37 passed. Real local Uvicorn processes show the module's IPv6 failure on base and HTTP 200 after the fix, with IPv4 loopback/wildcard and direct-Uvicorn IPv6 controls passing. All temporary servers were stopped.

Ruff, format checks, wheel/sdist build, Twine, offline wheel installation, and installed configuration/entrypoint smoke pass. The wheel's seven package source modules match the tested source.

Checklist

• My code follows the project's coding style
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published

Screenshots (if applicable)

Not applicable.

Additional Notes

Windows Python 3.12.14, Uvicorn 0.54.0 and cached dependencies. Validation covers local listeners and /health; no deployed OpenWebUI, actual OpenViking backend, live model, authentication, full server, minimum-version matrix, other OS or performance test. Existing license-metadata deprecation warnings remain. Main-server bind/retry logic and session-ID validation are outside this change.