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/pkm-curation/references/agent-integration.md

@@ -0,0 +1,51 @@
+---
+id: pkm-curation-agent-integration
+aliases:
+  - PKM Curation agent Integration
+tags:
+  - knowledge-management
+  - reference
+area: Personal Knowledge Management
+project:
+---
+
+# Agent Integration
+
+## Purpose
+
+This skill should be usable from any agent, and it should also fit chat environments where the agent as tool access.
+
+## Recommended Role
+
+- batch curation, targeted note cleanup, folder reviews, and repeatable vault maintenance
+- interactive note refinement, serendipity review, and exploratory linking sessions
+- editor-side entry point that delegates vault actions to agent where possible
+
+## Preferred Behaviors
+
+- search the vault before proposing links
+- inspect nearby notes before creating new ones
+- patch files directly when the requested change is clear
+- summarize edits in plain Markdown
+- ask before removing any content or links from a note
+- ask before moving, renaming, or creating many files
+
+## Good Task Shapes
+
+- curate a specific note
+- process a small `Inbox/` batch
+- review recent notes for missing links
+- extract atomic notes from one source note
+- run a serendipity review against a current topic
+
+## Avoid
+
+- large autonomous folder reorganizations
+- broad speculative linking passes
+- converting every long note into atomic notes
+- changing note titles without stating why
+
+## Portability Guidance
+
+- keep the workflow in `SKILL.md` tool-agnostic where possible
+- prefer small deterministic file edits so the skill remains portable to other `SKILL.md`-based agents