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>

.claude/skills/dolibarr-tva-summary/examples/tva-summary.txt

@@ -0,0 +1,29 @@
+# Arcodange TVA monthly summary — window=-inf → +inf
+# (composition of dolibarr-tva-reconciliation + dolibarr-tva-deductible)
+
+=== 2025-10 ===
+  Customer side (TVA collectée)   basis HT=      0.00   TVA=    0.00
+  Supplier side (TVA déductible)  basis HT=      6.08   TVA=    1.22
+      ligne 19/20 (20.0% déductible)              HT=      6.08  TVA=    1.22
+  --- Net du mois : collectée − déductible = 0.00 − 1.22 =    -1.22   → CRÉDIT DE TVA : 1.22 €
+
+=== 2026-01 ===
+  Customer side (TVA collectée)   basis HT=    510.00   TVA=    0.00
+      E2 (export hors UE)                         HT=    510.00  TVA=    0.00
+  Supplier side (TVA déductible)  basis HT=    403.45   TVA=   69.00
+      FR exempt / HT seulement                    HT=      8.43  TVA=    0.00
+      ligne 17+24 (autoliquidation intra-UE)      HT=     50.00  TVA=    0.00
+      ligne 19/20 (20.0% déductible)              HT=    345.02  TVA=   69.00
+  --- Net du mois : collectée − déductible = 0.00 − 69.00 =   -69.00   → CRÉDIT DE TVA : 69.00 €
+
+=== 2026-02 ===
+  Customer side (TVA collectée)   basis HT=   7650.00   TVA=    0.00
+      E2 (export hors UE)                         HT=   7650.00  TVA=    0.00
+  Supplier side (TVA déductible)  basis HT=    765.00   TVA=  153.00
+      ligne 19/20 (20.0% déductible)              HT=    765.00  TVA=  153.00
+  --- Net du mois : collectée − déductible = 0.00 − 153.00 =  -153.00   → CRÉDIT DE TVA : 153.00 €
+
+=== CUMUL window=-inf → +inf ===
+  TVA collectée totale  :       0.00
+  TVA déductible totale :     223.22
+  Net cumulé            :    -223.22   → CRÉDIT DE TVA cumulé : 223.22 €