add bin/arcodange CLI and dolibarr-tva-summary skill

Two changes that go together: now operators can run every read-only
workflow without going through Claude. The skills (SKILL.md files)
remain the source of behaviour documentation and Claude triggers;
bin/arcodange is the human-facing entry point.

bin/arcodange:
- Bash dispatcher at the project root. Subcommands per domain:
  tva {collect, collect-detail, deductible, deductible-detail, summary},
  invoice {list, audit}, thirdparty {audit, audit-all},
  payments {state, timeline, by-month},
  templates {list, inspect},
  snapshot, whoami, ping, curl, help.
- Locates the project root via `git rev-parse` so it works from any
  CWD (including from a worktree).
- Per-subcommand `help` text. Unknown commands exit 2 with a hint.
- Reuses the existing per-skill scripts under .claude/skills/<name>/
  scripts/ via `exec` (zero behaviour drift, full credit to the
  existing tested code).

dolibarr-tva-summary:
- Composes dolibarr-tva-reconciliation (TVA collectée customer-side)
  and dolibarr-tva-deductible (TVA déductible supplier-side) into a
  single CA3-ready monthly summary with per-month net verdict
  (TVA à reverser / crédit de TVA / équilibre) and a cumulative line.
- Live baseline: Arcodange en crédit de TVA de 223.22 € cumulé
  (0 € collectée 259-1° CGI vs 223.22 € déductible).
- Exposed as `arcodange tva summary [--year|--since|--until]`.

Each existing skill's SKILL.md gets a one-line "CLI shortcut" near
the top so the human path is discoverable from any skill page.
The project root README.md gets a CLI section as the primary
operator entry point.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

README.md

@@ -1,5 +1,29 @@
 # ERP
 
+## CLI — `bin/arcodange`
+
+Read-only operational CLI for the Arcodange Dolibarr at `erp.arcodange.lab`. One entry point, subcommands per domain:
+
+```sh
+bin/arcodange ping                          # Dolibarr version + liveness
+bin/arcodange whoami                        # confirm auth as ai_agent
+bin/arcodange invoice list                  # KissMetrics invoices with payment state
+bin/arcodange invoice audit 12              # JSON facts + PDF mandatory-mention audit
+bin/arcodange payments state                # per-invoice TTC vs payments reconciliation
+bin/arcodange payments timeline --year 2026 # cash receipts with cumulative balance
+bin/arcodange tva summary                   # CA3-ready collectée − déductible per month
+bin/arcodange thirdparty audit-all          # completeness audit, country-aware
+bin/arcodange templates inspect 1           # recurring template health (frequency, next fire, …)
+bin/arcodange snapshot --out /tmp/erp.json  # full state dump with content_hash
+bin/arcodange help                          # full command tree
+```
+
+**Read-only by design.** The underlying API key (`ai_agent`) has no write permissions; corrections go through the Dolibarr UI.
+
+**Credentials.** Reads `.claude/skills/dolibarr/.env` (mode 600, gitignored). Setup instructions: [.claude/skills/dolibarr/README.md](.claude/skills/dolibarr/README.md).
+
+**Source of behaviour.** Each subcommand delegates to a script under `.claude/skills/<skill>/scripts/`. The skills' `SKILL.md` files document the business logic and are also discoverable by Claude Code via skill triggers.
+
 ## Dolibarr
 
 ### Premiers démarrages