fix: allow plugin-registered agent roles in factory agent CLI

[shivchander]

Closes #1260

Changes

• Add BUILTIN_AGENT_ROLES frozenset in factory/cli/_parser_groups.py as the single source of truth for built-in roles
• Remove hardcoded choices from the argparse role argument — argparse no longer rejects unknown roles at parse time
• Add dynamic validation in cmd_agent() that checks the role against BUILTIN_AGENT_ROLES | plugin_registry.agent_roles, returning a clear error with valid role list
• Add agent_roles field and add_agent_roles() method to PluginRegistry in factory/plugins.py, following the same collision-guard pattern as add_modes()
• Show registered plugin agent roles in factory plugins output

[github-actions]

Sentrux Quality Report

Absolute

Scanning ....
[scan] git ls-files: 609 total, 597 kept, 12 dropped (ext:12, meta:0, big:0)
[build_project_map] 597 files, 102 unique dirs, 94 cache misses, 2.6ms
[resolve] 1091 resolved, 1537 unresolved (of 2628 total specs)
[resolve_imports] project_map 2.7ms, suffix_idx 0.9ms, suffix_resolve 11.8ms, total 15.4ms
[build_graphs] 597 files | maps 1.7ms, imports 15.5ms, calls+inherit 4.3ms, total 21.6ms | 1090 import, 8622 call, 11 inherit edges
sentrux check — 3 rules checked

Quality: 4694

✗ [Error] max_cc: 3 function(s) exceed max cyclomatic complexity of 30
    factory/cli/_ceo_helpers.py:_validate_ceo_flags (cc=43)
    factory/cli/_ceo_helpers.py:_execute_ceo (cc=43)
    factory/cli/run.py:cmd_run (cc=32)

✗ 1 violation(s) found

Diff (vs base branch)

Scanning ....
[scan] git ls-files: 609 total, 597 kept, 12 dropped (ext:12, meta:0, big:0)
[build_project_map] 597 files, 102 unique dirs, 94 cache misses, 2.5ms
[resolve] 1091 resolved, 1537 unresolved (of 2628 total specs)
[resolve_imports] project_map 2.7ms, suffix_idx 0.9ms, suffix_resolve 11.7ms, total 15.2ms
[build_graphs] 597 files | maps 1.8ms, imports 15.4ms, calls+inherit 4.9ms, total 22.2ms | 1090 import, 8622 call, 11 inherit edges
sentrux gate — structural regression check

Quality:      4790 -> 4694
Coupling:     0.79 → 0.79
Cycles:       3 → 3
God files:    3 → 3

Distance from Main Sequence: 0.38

✓ No degradation detected

[codecov]

Codecov Report

❌ Patch coverage is 39.13043% with 14 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.29%. Comparing base (4129ba2) to head (1b58e3f).

Files with missing lines	Patch %	Lines
factory/plugins.py	18.18%	9 Missing ⚠️
factory/cli/agents.py	57.14%	2 Missing and 1 partial ⚠️
factory/cli/_main.py	0.00%	2 Missing ⚠️

❌ Your patch check has failed because the patch coverage (39.13%) is below the target coverage (79.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1267      +/-   ##
==========================================
- Coverage   86.34%   86.29%   -0.05%     
==========================================
  Files         211      211              
  Lines       23054    23075      +21     
  Branches     3627     3632       +5     
==========================================
+ Hits        19906    19913       +7     
- Misses       2308     2321      +13     
- Partials      840      841       +1     

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