Remove Node.js hooks, require ots CLI only

- Delete hooks/post-commit-node (local proofs only, no attestation)
- Delete hooks/pre-commit-node (no upgrade support)
- Update hooks/install.sh to require ots CLI (no fallback)
- Update documentation with clear ots CLI requirement
- Add prominent warnings about Node.js limitations

Rationale: The @opentimestamps/ots Node.js package only creates
local proofs without calendar submission or Bitcoin attestation.
For tamper-evident timestamps, ots CLI is the only complete
implementation. No partial/fallback implementations.

SKILL.md

@@ -1,16 +1,40 @@
 ---
 name: git-ots-hook
-description: Install and manage OpenTimestamp git hooks that generate cryptographic proof for every commit. Use when you need to add tamper-evident timestamps to git commits using the OpenTimestamp protocol. Auto-detects ots CLI (recommended) or Node.js package.
+description: Install and manage OpenTimestamp git hooks that generate cryptographic proof for every commit. Requires opentimestamps-client (ots CLI) for full Bitcoin attestation.
 ---
 
 # Git OpenTimestamp Hook
 
 Automatically generates OpenTimestamp proofs for git commits via git hooks.
 
+## ⚠️ Prerequisites (Required)
+
+**You must have `ots` CLI installed:**
+
+```bash
+# Recommended (isolated install)
+pipx install opentimestamps-client
+
+# Or with pip
+pip install opentimestamps-client
+
+# Or from source
+git clone https://github.com/opentimestamps/opentimestamps-client
+cd opentimestamps-client && pip install .
+```
+
+**Verify installation:**
+```bash
+ots --version
+# v0.7.2 or later
+```
+
+> **Why ots CLI is required:** The Node.js `@opentimestamps/ots` package only creates local proofs without calendar submission or Bitcoin attestation. For tamper-evident timestamps anchored to Bitcoin, the Python `opentimestamps-client` is the only complete implementation.
+
 ## Quick Start
 
 ```bash
-# Install both hooks (auto-detects ots CLI or Node.js)
+# Install both hooks (requires ots CLI)
 ./hooks/install.sh /path/to/repo
 
 # Or from repo root
@@ -18,32 +42,18 @@ Automatically generates OpenTimestamp proofs for git commits via git hooks.
 ```
 
 The installer will:
-1. Detect available tools (ots CLI preferred, Node.js fallback)
-2. Install matching hooks
-3. Setup `.gitignore` (excludes cache + node_modules)
-4. Install `@opentimestamps/ots` locally if using Node.js mode
+1. Verify `ots` CLI is installed
+2. Install post-commit and pre-commit hooks
+3. Setup `.gitignore` (excludes cache file)
 
 ## What It Does
 
-- **Auto-detects tools**: ots CLI (full Bitcoin attestation) or Node.js package (local proofs only)
 - **Post-commit hook**: Generates `.ots/<commit-hash>.ots` for each new commit
-- **Pre-commit backfill**: Upgrades historical proofs to attested status (ots CLI only)
+- **Pre-commit backfill**: Upgrades historical proofs to Bitcoin-attested status
 - Creates `.ots/proof.ots` (latest proof reference)
 - Stores commit chain in `.ots/commit-chain.txt`
 - Smart caching: Skips calendar calls for recently checked proofs
-
-## Prerequisites
-
-**Option 1: ots CLI (Recommended - Full Bitcoin attestation)**
-```bash
-pipx install opentimestamps-client
-```
-
-**Option 2: Node.js (Local proofs only)**
-```bash
-# Package will be installed locally by the installer
-# Or globally: npm install -g @opentimestamps/ots
-```
+- Submits to 4+ remote calendar servers for Bitcoin anchoring
 
 ## Generated Files
 
@@ -58,32 +68,39 @@ repo/
 └── ...
 ```
 
-## Manual Usage
+## Manual Installation
 
-**Install hooks (auto-detect):**
-```bash
-./hooks/install.sh /path/to/repo
-```
+If you prefer manual setup:
 
-**Manual installation:**
 ```bash
-# For ots CLI:
 cp hooks/post-commit-ots .git/hooks/post-commit
 cp hooks/pre-commit-ots .git/hooks/pre-commit
-
-# For Node.js:
-cp hooks/post-commit-node .git/hooks/post-commit
-cp hooks/pre-commit-node .git/hooks/pre-commit
-
 chmod +x .git/hooks/post-commit .git/hooks/pre-commit
 ```
 
+Add to `.gitignore`:
+```
+.ots/.attestation-cache
+```
+
+## Manual Usage
+
 **Check attestation status:**
 ```bash
 ots info .ots/<commit-hash>.ots | grep -c "PendingAttestation"
 # 0 = attested, >0 = pending
 ```
 
+**Verify a proof:**
+```bash
+ots verify .ots/<commit-hash>.ots
+```
+
+**Upgrade pending proofs:**
+```bash
+ots upgrade .ots/<commit-hash>.ots
+```
+
 ## Notes
 
 ### Versioning Proofs
@@ -101,28 +118,39 @@ git commit -m "Add OpenTimestamp proofs"
 
 **Ignore these:**
 - `.attestation-cache` - Local performance cache
-- `node_modules/` - If using Node.js mode (auto-added by installer)
 
 ### Performance
 
 - **First backfill:** ~30-60s (scans history, contacts calendars)
 - **Subsequent commits:** ~10-15s (cached status skips redundant calls)
-- **Cache:** 1-hour validity, 10-min recheck for pending proofs
+- **Cache:** 1-hour validity, re-checks pending proofs after 10 min
+- **Attestation time:** ~10 min (Bitcoin block confirmation)
 
-### Modes
+### How It Works
 
-| Feature | ots CLI | Node.js |
-|---------|---------|---------|
-| Calendar submission | ✓ | ✗ |
-| Bitcoin attestation | ✓ | ✗ |
-| Local proofs | ✓ | ✓ |
-| Upgrade support | ✓ | ✗ |
-| Speed | Fast | Fast |
+1. **Commit created** → Post-commit hook runs
+2. **Hash generated** → SHA256 of commit hash
+3. **Submitted to calendars** → 4+ remote servers receive hash
+4. **Bitcoin anchoring** → Calendars batch and anchor to Bitcoin
+5. **Attestation** → `ots upgrade` downloads Bitcoin proof
+6. **Verification** → Anyone can verify against Bitcoin blockchain
 
-**Recommendation:** Use ots CLI for production. Node.js for development/testing only.
+### Calendar Servers
+
+Default calendars used:
+- `https://a.pool.opentimestamps.org`
+- `https://b.pool.opentimestamps.org`
+- `https://a.pool.eternitywall.com`
+- `https://btc.calendar.catallaxy.com`
 
 ## Uninstall
 
 ```bash
 rm .git/hooks/post-commit .git/hooks/pre-commit
 ```
+
+## Links
+
+- [OpenTimestamp](https://opentimestamps.org/)
+- [opentimestamps-client](https://github.com/opentimestamps/opentimestamps-client)
+- [How OpenTimestamp works](https://petertodd.org/2016/opentimestamps-announcement)