feat: initialize agent skills repository with three starter skills

Add project structure documentation (AGENTS.md) and initial README files
that organize skills by bucket and invocation type (user-invoked vs
model-invoked).

Introduce three skills:
- forge-interaction: GitHub/Gitea CLI automation for issues, PRs, releases
- forge-preferences: personal forge conventions (companion to forge-interaction)
- pkm-curation: Obsidian vault curation and note management

Include reference docs for vault conventions, agent integration, and the
invocation model that separates user-only from model-reachable skills.

common/personal/forge-preferences/SKILL.md

@@ -0,0 +1,31 @@
+---
+name: forge-preferences
+description: Use with forge-interaction to apply Steve's personal or project-specific GitHub/Gitea remote, CLI, issue, PR, and release preferences.
+---
+
+# Forge Preferences
+
+Use this companion skill with `/forge-interaction` when personal or project-specific forge preferences are relevant.
+
+## Purpose
+
+Store personal conventions that should not live in the generic forge interaction skill.
+
+## Current Preferences
+
+- If a remote named `forge` exists, treat it as the canonical forge remote.
+- If no `forge` remote exists, use the user's configured default remote when available.
+- If no default remote is configured, use `origin`.
+- Use the forge type of the selected remote to choose the CLI:
+  - GitHub → `gh`
+  - Gitea → `tea`
+- If the correct CLI is missing, tell the user to install it or add it to `PATH`.
+- Do not use the wrong CLI as a fallback.
+
+## Open Questions To Fill In Later
+
+- Known personal Gitea hosts.
+- GitHub usernames or organizations.
+- Preferred PR title/body format.
+- Preferred issue labels and milestones.
+- Release naming and tagging conventions.