feat(context-provider): add support for indexing multiple branches

[zwpaper]

git

1. auto detect branch by default: https://jam.dev/c/10f42266-b492-4857-8569-c790723c7cb5
2. create with multiple branches: https://jam.dev/c/13c907de-a8db-48a3-84c4-97f7ddbb5785
   1. retrieve from other branch
   2. multiple branch in code browser
3. update branches: https://jam.dev/c/53216f3c-7510-4657-bbb8-d1b5e45a422c
   1. added new branch in code browser

github

1. auto detect branch: https://jam.dev/c/7ec2d83a-79db-4994-95b3-ea9b9178fa44
2. create with multiple branches: https://jam.dev/c/4d2d5628-3201-4a52-99d0-fc40777d14a0
   1. context from other branch:
   2. code browser
3. update branch: https://jam.dev/c/7e0bc271-3ef8-4cca-bd7d-67c8f5b3429c

[codecov]

Codecov Report

❌ Patch coverage is 36.70588% with 269 lines in your changes missing coverage. Please review.
✅ Project coverage is 54.48%. Comparing base (702240a) to head (a7bd789).

Files with missing lines	Patch %	Lines
crates/tabby-index/src/code/repository.rs	0.00%	62 Missing ⚠️
crates/tabby-git/src/lib.rs	0.00%	49 Missing ⚠️
ee/tabby-schema/src/schema/mod.rs	0.00%	31 Missing ⚠️
...by-webserver/src/service/repository/third_party.rs	41.66%	28 Missing ⚠️
ee/tabby-db/src/provided_repositories.rs	47.82%	24 Missing ⚠️
crates/tabby-index/src/code/index.rs	0.00%	23 Missing ⚠️
ee/tabby-webserver/src/service/repository/mod.rs	46.66%	16 Missing ⚠️
ee/tabby-webserver/src/service/repository/git.rs	70.45%	13 Missing ⚠️
.../tabby-webserver/src/service/background_job/git.rs	0.00%	9 Missing ⚠️
crates/tabby-common/src/axum.rs	60.00%	4 Missing ⚠️
... and 4 more

❌ Your patch check has failed because the patch coverage (36.70%) is below the target coverage (75.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4419      +/-   ##
==========================================
- Coverage   55.16%   54.48%   -0.69%     
==========================================
  Files         229      227       -2     
  Lines       27043    27035       -8     
==========================================
- Hits        14919    14729     -190     
- Misses      12124    12306     +182     

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[liangfung]

After connecting a local repository without specifying a branch, it incorrectly indexes all branches instead of only the default branch.

The “Edit Repository” dialog has styling issues.