chore: add shared agent skills (#20)

Adds the shared agent-skill core under `.agents/skills/` (grilling, grill-me, domain-modeling, codebase-design, code-review, diagnosing-bugs, tdd, research, implement, handoff), with `.claude` symlinked to `.agents` so every agent harness picks them up.

Project-local skills are left untouched. The runtime `scheduled_tasks.lock` is deliberately not committed.

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Reviewed-on: #20
Reviewed-by: xtul <mpiasecki720@protonmail.com>
Co-authored-by: vickydotbat <vickydotbat@tutamail.com>
Co-committed-by: vickydotbat <vickydotbat@tutamail.com>

.agents/skills/research/SKILL.md

@@ -0,0 +1,12 @@
+---
+name: research
+description: Investigate a question against high-trust primary sources and capture the findings as a Markdown file in the repo. Use when the user wants a topic researched, docs or API facts gathered, or reading legwork delegated to a background agent.
+---
+
+Spin up a **background agent** to do the research, so you keep working while it reads.
+
+Its job:
+
+1. Investigate the question against **primary sources** — official docs, source code, specs, first-party APIs — not a secondary write-up of them. Follow every claim back to the source that owns it.
+2. Write the findings to a single Markdown file, citing each claim's source.
+3. Save it where the repo already keeps such notes; match the existing convention, and if there is none, put it somewhere sensible and say where.