Better mTLS support

[denysvitali]

Description

As per #15230 - the mTLS support (and User-CA support) in Immich is rather poor.
This PR (DRAFT!) will fix these issues by integrating ok_http and using the Android trust store.

Fixes #15230

This PR depends on two PRs opened at dart-lang/http:

• fix(ok_http): trust manager init dart-lang/http#1830
• feat(ok_http): add user-agent dart-lang/http#1831

How Has This Been Tested?

N/A

Screenshots (if appropriate)

Checklist:

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation if applicable
• I have no unrelated changes in the PR.
• I have confirmed that any new dependencies are strictly necessary.
• I have written tests for new code (if applicable)
• I have followed naming conventions/patterns in the surrounding code
• All code in src/services/ uses repositories implementations for database calls, filesystem operations, etc.
• All code in src/repositories/ is pretty basic/simple and does not have any immich specific logic (that belongs in src/services/)

Please describe to which degree, if any, an LLM was used in creating this pull request.

Extensively. Mostly Z.AI GLM 4.6.

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