feat(mcp): add list_tags and get_tag_info MCP tools

[aminghadersohi]

SUMMARY

Adds list_tags and get_tag_info MCP tools in a new superset/mcp_service/tag/ domain, following the established pattern used by the database, dataset, and dashboard domains.

New files:

• superset/mcp_service/tag/__init__.py
• superset/mcp_service/tag/schemas.py — TagFilter, TagInfo, TagList, ListTagsRequest, GetTagInfoRequest, TagError, serialize_tag_object()
• superset/mcp_service/tag/tool/list_tags.py — list tags with filtering, search, pagination
• superset/mcp_service/tag/tool/get_tag_info.py — get a single tag by numeric ID
• tests/unit_tests/mcp_service/tag/tool/test_tag_tools.py — unit tests covering basic listing, search, filters, empty results, error handling, not-found, and type serialization

Both tools are registered in app.py.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

N/A — MCP tool additions only.

TESTING INSTRUCTIONS

1. Run unit tests:

   pytest tests/unit_tests/mcp_service/tag/

2. Start the MCP server and verify list_tags and get_tag_info appear in the tool list.
3. Call list_tags with no arguments — should return the first page of tags.
4. Call get_tag_info with a valid tag ID — should return tag name, type, and description.

ADDITIONAL INFORMATION

• Has associated issue:
• Required feature flags:
• Changes UI
• Includes DB Migration
• Introduces new feature or API
• Introduces new feature or API — adds two new MCP tools for tag discovery
• Removes existing feature or API

[codecov]

Codecov Report

❌ Patch coverage is 62.16216% with 56 lines in your changes missing coverage. Please review.
✅ Project coverage is 64.14%. Comparing base (f187a8e) to head (ba361ff).
⚠️ Report is 9 commits behind head on master.

Files with missing lines	Patch %	Lines
superset/mcp_service/tag/schemas.py	73.56%	22 Missing and 1 partial ⚠️
superset/mcp_service/tag/tool/list_tags.py	39.39%	20 Missing ⚠️
superset/mcp_service/tag/tool/get_tag_info.py	43.47%	13 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #40300      +/-   ##
==========================================
- Coverage   64.14%   64.14%   -0.01%     
==========================================
  Files        2592     2596       +4     
  Lines      138841   138993     +152     
  Branches    32201    32209       +8     
==========================================
+ Hits        89064    89160      +96     
- Misses      48245    48300      +55     
- Partials     1532     1533       +1     

Flag	Coverage Δ
hive	39.38% <62.16%> (+0.05%)	⬆️
mysql	58.86% <62.16%> (+0.01%)	⬆️
postgres	58.95% <62.16%> (+0.01%)	⬆️
presto	41.05% <62.16%> (+0.05%)	⬆️
python	60.50% <62.16%> (+<0.01%)	⬆️
sqlite	58.59% <62.16%> (+0.01%)	⬆️
unit	100.00% <ø> (ø)

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