H-289: add Captain Skill management API (#46)

* H-289: add Captain Skill management API

* H-289: guard Captain Skill updates with CAS

* H-289: version all Captain Skill updates

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Co-authored-by: Rogee <rogee@ipao.vip>

backend/migrations/000080_add_captain_skills.down.sql

@@ -0,0 +1,3 @@
+DROP TABLE IF EXISTS captain_assistant_skills;
+DROP TABLE IF EXISTS captain_skill_references;
+DROP TABLE IF EXISTS captain_skills;

backend/migrations/000080_add_captain_skills.up.sql

@@ -0,0 +1,38 @@
+CREATE TABLE captain_skills (
+    id SERIAL PRIMARY KEY,
+    account_id INTEGER NOT NULL REFERENCES accounts(id) ON DELETE CASCADE,
+    name VARCHAR(255) NOT NULL,
+    description VARCHAR(1024) NOT NULL,
+    instructions_md TEXT NOT NULL,
+    status VARCHAR(20) NOT NULL DEFAULT 'draft' CHECK (status IN ('draft', 'active', 'archived')),
+    version INTEGER NOT NULL DEFAULT 1 CHECK (version > 0),
+    created_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    updated_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    UNIQUE (account_id, name)
+);
+
+CREATE INDEX idx_captain_skills_account_status ON captain_skills(account_id, status);
+
+CREATE TABLE captain_skill_references (
+    id SERIAL PRIMARY KEY,
+    skill_id INTEGER NOT NULL REFERENCES captain_skills(id) ON DELETE CASCADE,
+    reference_key VARCHAR(255) NOT NULL,
+    content_md TEXT NOT NULL,
+    position INTEGER NOT NULL CHECK (position >= 0),
+    created_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    updated_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    UNIQUE (skill_id, reference_key),
+    UNIQUE (skill_id, position)
+);
+
+CREATE TABLE captain_assistant_skills (
+    id SERIAL PRIMARY KEY,
+    account_id INTEGER NOT NULL REFERENCES accounts(id) ON DELETE CASCADE,
+    assistant_id INTEGER NOT NULL REFERENCES captain_assistants(id) ON DELETE CASCADE,
+    skill_id INTEGER NOT NULL REFERENCES captain_skills(id) ON DELETE CASCADE,
+    created_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    UNIQUE (assistant_id, skill_id)
+);
+
+CREATE INDEX idx_captain_assistant_skills_account ON captain_assistant_skills(account_id);
+CREATE INDEX idx_captain_assistant_skills_skill ON captain_assistant_skills(skill_id);