Add sharing API and UI for collections

[BenjaminCharmes]

Closes #1524

Changes:

• Add permission editors to collection edit page
• Add group/creator selectors to collection creation modal
• Add PATCH /collections/<id>/permissions endpoint
• Include groups lookup in collection GET requests

Collections now support the same permission system as items, with groups providing read-only access and creators having read-write access.

When a user has access to a collection as a creator or via group membership, they also get read access to the items within.

[codecov]

Codecov Report

❌ Patch coverage is 83.72093% with 14 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.88%. Comparing base (ce4f17c) to head (2f82e1d).

Files with missing lines	Patch %	Lines
pydatalab/src/pydatalab/routes/v0_1/collections.py	82.19%	13 Missing ⚠️
pydatalab/src/pydatalab/permissions.py	91.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1564      +/-   ##
==========================================
+ Coverage   78.82%   78.88%   +0.05%     
==========================================
  Files          81       81              
  Lines        7038     7118      +80     
==========================================
+ Hits         5548     5615      +67     
- Misses       1490     1503      +13     

Files with missing lines	Coverage Δ
pydatalab/src/pydatalab/routes/v0_1/items.py	83.01% <100.00%> (ø)
pydatalab/src/pydatalab/permissions.py	89.47% <91.66%> (+0.15%)	⬆️
pydatalab/src/pydatalab/routes/v0_1/collections.py	78.53% <82.19%> (+1.87%)	⬆️

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[cypress]

datalab    Run #4862

Run Properties:   Passed #4862  •  9db6c765e4 ℹ️: Merge 2f82e1d6651e979b7f6b7077345f0c6f32367297 into ce4f17ca0b26aa74d6566c001b4a...

Project	datalab
Branch Review	bc/ui-sharing-col
Run status	Passed #4862
Run duration	09m 44s
Commit	9db6c765e4 ℹ️: Merge 2f82e1d6651e979b7f6b7077345f0c6f32367297 into ce4f17ca0b26aa74d6566c001b4a...
Committer	Ben Charmes
View all properties for this run ↗︎

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Test results
Failures	0
Flaky	0
Pending	0
Skipped	0
Passing	478
View all changes introduced in this branch ↗︎