feat: structured skills system with meta skill runtime injection

Replace agent.skills TEXT field with structured skill/skill_file/agent_skill
tables. Skills are workspace-level entities with supporting files, reusable
across agents via many-to-many bindings.

Backend: migration 008, sqlc queries, CRUD handler, agent-skill junction,
structured skill loading in task context snapshot.

Daemon: meta skill injection via runtime-native config (.claude/CLAUDE.md
for Claude, AGENTS.md for Codex) so agents discover .agent_context/ skills
through their native mechanism. Lean prompt without inlined skill content.

Frontend: Skills management page, agent Skills tab picker, SDK methods,
TypeScript types, workspace store integration.

Also removes auto-creation of init issues when creating agents.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/pkg/db/queries/skill.sql

@@ -0,0 +1,80 @@
+-- Skill CRUD
+
+-- name: ListSkillsByWorkspace :many
+SELECT * FROM skill
+WHERE workspace_id = $1
+ORDER BY name ASC;
+
+-- name: GetSkill :one
+SELECT * FROM skill
+WHERE id = $1;
+
+-- name: CreateSkill :one
+INSERT INTO skill (workspace_id, name, description, content, config, created_by)
+VALUES ($1, $2, $3, $4, $5, $6)
+RETURNING *;
+
+-- name: UpdateSkill :one
+UPDATE skill SET
+    name = COALESCE(sqlc.narg('name'), name),
+    description = COALESCE(sqlc.narg('description'), description),
+    content = COALESCE(sqlc.narg('content'), content),
+    config = COALESCE(sqlc.narg('config'), config),
+    updated_at = now()
+WHERE id = $1
+RETURNING *;
+
+-- name: DeleteSkill :exec
+DELETE FROM skill WHERE id = $1;
+
+-- Skill File CRUD
+
+-- name: ListSkillFiles :many
+SELECT * FROM skill_file
+WHERE skill_id = $1
+ORDER BY path ASC;
+
+-- name: GetSkillFile :one
+SELECT * FROM skill_file
+WHERE id = $1;
+
+-- name: UpsertSkillFile :one
+INSERT INTO skill_file (skill_id, path, content)
+VALUES ($1, $2, $3)
+ON CONFLICT (skill_id, path) DO UPDATE SET
+    content = EXCLUDED.content,
+    updated_at = now()
+RETURNING *;
+
+-- name: DeleteSkillFile :exec
+DELETE FROM skill_file WHERE id = $1;
+
+-- name: DeleteSkillFilesBySkill :exec
+DELETE FROM skill_file WHERE skill_id = $1;
+
+-- Agent-Skill junction
+
+-- name: ListAgentSkills :many
+SELECT s.* FROM skill s
+JOIN agent_skill ask ON ask.skill_id = s.id
+WHERE ask.agent_id = $1
+ORDER BY s.name ASC;
+
+-- name: AddAgentSkill :exec
+INSERT INTO agent_skill (agent_id, skill_id)
+VALUES ($1, $2)
+ON CONFLICT DO NOTHING;
+
+-- name: RemoveAgentSkill :exec
+DELETE FROM agent_skill
+WHERE agent_id = $1 AND skill_id = $2;
+
+-- name: RemoveAllAgentSkills :exec
+DELETE FROM agent_skill WHERE agent_id = $1;
+
+-- name: ListAgentSkillsByWorkspace :many
+SELECT ask.agent_id, s.id, s.name, s.description
+FROM agent_skill ask
+JOIN skill s ON s.id = ask.skill_id
+WHERE s.workspace_id = $1
+ORDER BY s.name ASC;