fix(spawn): add pi to profile model flag resolution

[ruttybob]

Summary

When a profile specifies --agent pi --model X, the model is silently ignored because _model_flag() in profiles.py did not include "pi" in its agent set.

Changes

• clawteam/spawn/profiles.py — Add "pi" to _model_flag() so --model is appended from profile.model. Add explicit return None entries for pi in _base_url_env_var() and _api_key_target_env() (pi resolves these via --provider and provider-specific env vars, not a single base-url/api-key env).
• tests/test_profiles.py — Add 3 new tests:
  • test_apply_profile_pi_model_flag_is_injected — verifies --model is appended
  • test_apply_profile_pi_model_not_duplicated_when_already_present — verifies no double --model
  • test_apply_profile_pi_no_base_url_or_api_key_env_injection — verifies pi does not auto-inject env vars

Test Results

All 445 tests pass (2 skipped due to missing mcp module, unrelated to this change):

tests/test_adapters.py ...................                                [  4%]
tests/test_board.py ..............                                       [  7%]
tests/test_cli_commands.py ................                              [ 11%]
tests/test_config.py ..............                                      [ 14%]
tests/test_context.py ..                                                 [ 14%]
tests/test_costs.py ...........                                          [ 17%]
tests/test_fileutil.py ..........                                        [ 19%]
tests/test_gource.py .....                                               [ 20%]
tests/test_identity.py ...............                                   [ 23%]
tests/test_inbox_routing.py ..                                           [ 24%]
tests/test_lifecycle.py .......                                          [ 25%]
tests/test_mailbox.py ..............................                     [ 32%]
tests/test_manager.py .............................                      [ 39%]
tests/test_models.py ..................                                  [ 43%]
tests/test_plan_storage.py .....                                         [ 44%]
tests/test_presets.py ........                                           [ 46%]
tests/test_profiles.py ...........                                       [ 47%]  ← was 8, now 11
tests/test_prompt.py .........                                           [ 49%]
tests/test_registry.py ......................                            [ 54%]
tests/test_runtime_routing.py ..........                                 [ 57%]
tests/test_snapshots.py .....................                            [ 61%]
tests/test_spawn_backends.py .......................................     [ 70%]
tests/test_spawn_cli.py .................                                [ 74%]
tests/test_store.py ..................                                   [ 78%]
tests/test_task_store_locking.py .                                       [ 78%]
tests/test_tasks.py ............................................         [ 88%]
tests/test_templates.py .........................                        [ 94%]
tests/test_timefmt.py ...                                                [ 94%]
tests/test_waiter.py ...................                                 [ 99%]
tests/test_workspace_manager.py .                                        [ 99%]
tests/test_wsh_backend.py ...                                            [100%]

======================= 445 passed in 143.36s ========================

Usage Example

# Create a profile for Pi with a specific model
clawteam profile set pi-anthropic \
  --agent pi \
  --model "anthropic/claude-sonnet-4.6"

# Spawn an agent — --model is now correctly appended
clawteam spawn tmux --profile pi-anthropic --team myteam --task "Implement feature X"
# Results in: pi --model anthropic/claude-sonnet-4.6 -p "..."