Feature/support for vertexai accounts

[giefferre]

Summary

Add first-class Google VertexAI account support alongside existing OAuth accounts. CCM can now manage mixed fleets of OAuth and VertexAI identities with full feature parity: switching, isolated profiles, export/import, health checks, and statusline display.

Motivation

Claude Code supports authentication via Google VertexAI (CLAUDE_CODE_USE_VERTEX=1 in settings.json), but CCM's account model was built entirely around OAuth email-based identity. Users running VertexAI cannot use CCM at all — ccm add fails because no .oauthAccount exists. This PR makes VertexAI a first-class account type, identified by GCP project ID instead of email.

Design decisions

• Auto-detection over manual flags: ccm add reads settings.json for CLAUDE_CODE_USE_VERTEX=1 and branches automatically — no --type vertex flag needed.
• Full env block as credential: The entire VertexAI env var set from settings.json (project ID, region, model pins, caching flags, service account path) is captured and restored as a unit, preserving configuration fidelity across switches.
• Clean transitions: Switching between OAuth and VertexAI removes the inactive type's configuration (.oauthAccount or VertexAI env vars) to prevent ambiguous auth state.
• Display format: VertexAI accounts render as vertex:project-id everywhere (list, statusline, history, export).

Changes

ccm.sh (+1114 / -375 lines):

• Schema bump 3.1 → 4.0 with additive migration (adds "type": "oauth" to existing accounts)
• ~10 new VertexAI helper functions: get_account_type(), get_account_display_id(), get_current_account_type(), read_vertex_env() / write_vertex_env() / clear_vertex_env(), credential backup/restore, account_exists_by_project(), validate_vertex_project_id()
• Type-aware perform_switch() dispatching four scenarios: OAuth↔OAuth, OAuth→Vertex, Vertex→OAuth, Vertex↔Vertex
• cmd_add_account() refactored into _add_oauth_account() + _add_vertex_account()
• Updated: cmd_list, cmd_verify, cmd_remove_account, cmd_export, cmd_import, cmd_reorder, cmd_recover, switch_isolated, profiles_sync, cmd_history, cmd_setup, embedded statusline heredoc
• resolve_account_identifier() now searches by project ID (4th dimension after number, email, alias)

statusline.sh: Mirrored VertexAI detection from embedded heredoc — reads CLAUDE_CODE_USE_VERTEX and ANTHROPIC_VERTEX_PROJECT_ID from settings.json, matches against sequence.json by .projectId.

Documentation: CHANGELOG.md, README.md, CLAUDE.md, ccm/SKILL.md, index.html, statusline.html updated with VertexAI references, examples, and corrected architecture line ranges.

Retro-compatibility

• Existing OAuth accounts are unaffected. The schema migration is purely additive.
• All existing commands, flags, and output formats are preserved for OAuth accounts.
• bash -n ccm.sh passes on every commit.

Test plan

• ccm version — shows 4.3.0
• ccm doctor — all 13 checks pass
• ccm list — existing OAuth accounts display normally with type: "oauth" after migration
• Configure a VertexAI session in settings.json, run ccm add — auto-detects and registers as vertex type
• ccm list — shows vertex:project-id for VertexAI account
• ccm switch between OAuth and VertexAI — clean transition, correct config state
• ccm switch --isolated <vertex-alias> — creates profile with correct env vars
• ccm verify — validates both OAuth and VertexAI backups
• ccm recover — detects VertexAI-specific inconsistencies
• ccm export / ccm import round-trip with mixed account types
• ccm remove <vertex-account> — cleans up vertex env backup and config
• Statusline displays vertex:project-id for active VertexAI session
• index.html and statusline.html render correctly in browser