feat: Add Tabnine CLI agent support

[Pavel-tabnine]

Add comprehensive support for Tabnine CLI as a new AI agent option:

• Add Tabnine CLI to AGENT_CONFIG with TOML format support
• Update CLI help text to include 'tabnine' as an option
• Add Tabnine CLI to README.md supported agents table with example
• Update AGENTS.md documentation:
  • Add to Current Supported Agents table
  • Add to CLI-Based Agents list
  • Update TOML format section
• Update release package scripts:
  • Add 'tabnine' to ALL_AGENTS array
  • Add case statement for .tabnine/commands/ directory structure
  • Add package entries to create-github-release.sh
• Update agent context update scripts (bash and PowerShell):
  • Add TABNINE_FILE variable
  • Add 'tabnine' case to update functions
  • Update usage documentation

Tabnine CLI uses the same TOML command format as Gemini and Qwen, with {{args}} placeholder and .tabnine/commands/ directory structure.

[github-actions]

Code Review Summary

✅ Overall Assessment: The implementation correctly adds Tabnine CLI support following established patterns across all relevant files.

What Works Well:

• Comprehensive coverage: All necessary files updated (CLI, scripts, documentation, release)
• Pattern consistency: Follows the exact same patterns as Gemini/Qwen for TOML format
• Cross-platform support: Both bash and PowerShell scripts updated consistently
• Proper validation: Added to ValidateSet and command help text

Critical Issue Identified:

Documentation Inconsistency (Pre-existing): The AGENTS.md file contains an outdated ALL_AGENTS array example on line 115 that shows only 8 agents instead of the current 16. This doesn't include tabnine or many other recent agents. While not caused by this PR, this should be fixed to prevent contributor confusion.

Recommendation:

The Tabnine CLI integration is correctly implemented and ready to merge. Consider updating the documentation inconsistency in a follow-up PR to keep the examples accurate.

[github-actions]

Critical Cross-Platform Issue: The PowerShell release script is missing the tabnine agent in multiple places:

1. Line 358: $AllAgents array does not include tabnine
2. Missing switch case in the Build-Variant function for tabnine
3. Line 17: Help text documentation is missing tabnine

Additionally, the shai agent (which appears to have been added previously) is also missing from all these locations in the PowerShell script, indicating a pattern of the PowerShell script not being updated when new agents are added.

This will cause PowerShell-based release builds to fail when trying to package Tabnine templates, breaking cross-platform compatibility.

Required Fix: Update .github/workflows/scripts/create-release-packages.ps1 to include both shai and tabnine agents matching the bash script implementation.

[github-actions]

Code Review Summary

What this PR accomplishes:
✅ Adds comprehensive Tabnine CLI agent support across the entire codebase
✅ Updates Python CLI configuration, help text, and agent mappings
✅ Adds proper documentation in README.md and AGENTS.md
✅ Updates bash scripts for context updates and release packaging
✅ Follows established patterns using TOML format and {{args}} placeholders

Critical Issue Found:
❌ Cross-platform compatibility broken: The PowerShell release script (.github/workflows/scripts/create-release-packages.ps1) was not updated to include the tabnine agent, and also appears to be missing the previously-added shai agent. This will cause PowerShell-based release builds to fail.

Resolution Required:
The PowerShell script must be updated to match the bash script implementation for both shai and tabnine agents in:

• $AllAgents array
• Build-Variant switch statement
• Help documentation

Once this cross-platform issue is resolved, the PR will provide complete and consistent Tabnine CLI support across the entire toolkit.