feat: add --dev flag to extension update command

[Testimonial]

Summary

• Adds --dev flag to specify extension update for local directory updates
• Eliminates the common dev workflow pain: rm -rf && git clone && remove && add --dev
• Now just: git pull && specify extension update --dev /path

Problem

Dev-installed extensions (specify extension add --dev /path) cannot be updated without a full remove + add cycle. The update command only checks the catalog, so locally-installed extensions get "Not found in catalog (skipping)".

Common workaround:

rm -rf /tmp/cognitive-squad
git clone https://github.com/org/cognitive-squad.git /tmp/cognitive-squad
specify extension remove cognitive-squad
specify extension add --dev /tmp/cognitive-squad

This destroys any local config files and resets registry metadata (installed_at, priority).

Solution

# Pull latest changes in local repo
cd /tmp/cognitive-squad && git pull

# Update the installed extension from local directory
specify extension update --dev /tmp/cognitive-squad

When --dev is specified:

1. Reads extension.yml from source directory to identify the extension
2. If not installed: installs fresh (same as add --dev)
3. If installed: backs up config files, removes old, installs from source, restores config + registry metadata
4. Preserves: installed_at, priority, enabled state, *-config.yml, *-config.local.yml, local-config.yml
5. Sets source: "local" in registry

No changes to the catalog update code path when --dev is not used.

Test plan

• specify extension update --dev /path/to/ext updates an installed dev extension
• specify extension update --dev /path/to/new-ext installs if not yet installed
• specify extension update --dev (no path) prints usage error
• specify extension update --dev /nonexistent prints directory not found error
• Config files preserved across dev update
• Registry metadata (installed_at, priority) preserved
• specify extension update ext-name (no --dev) still uses catalog (unchanged)

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