feat(enhance): config, templates, ComfyUI client, jobs, endpoints (#192)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

migrations/2026-10-30-100000_add_enhance_jobs/down.sql

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+DROP TABLE IF EXISTS enhance_jobs;

migrations/2026-10-30-100000_add_enhance_jobs/up.sql

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+-- Enhance on demand (#192): one row per ComfyUI run submitted for a photo.
+--
+-- Keyed to the photo by `original_hash` (the blake3 content_hash of the file
+-- that was submitted), like every other derived table, so a job survives a
+-- rename or move; `library_id` + `rel_path` say which file it was at submit
+-- time (and are what the API echoes back as `path`).
+CREATE TABLE enhance_jobs (
+    id              TEXT PRIMARY KEY NOT NULL,   -- uuid, ImageApi's own
+    original_hash   TEXT NOT NULL,
+    library_id      INTEGER NOT NULL,
+    rel_path        TEXT NOT NULL,
+    template        TEXT NOT NULL,
+    prompt          TEXT,
+    reference_hash  TEXT,
+    reference_path  TEXT,                        -- library-relative, same library
+    comfy_prompt_id TEXT NOT NULL,
+    -- queued | running | ready | approved | failed | expired | unavailable
+    status          TEXT NOT NULL,
+    error           TEXT,
+    queue_position  INTEGER,
+    -- json: [{id, view: {filename, subfolder, type}}], ComfyUI's staged results
+    pending         TEXT NOT NULL DEFAULT '[]',
+    -- json: [{n, comfy_path, library_id, rel_path}], approved results
+    saved           TEXT NOT NULL DEFAULT '[]',
+    -- 1 = the user threw the result away; hidden from the per-photo list
+    discarded       INTEGER NOT NULL DEFAULT 0,
+    created_at      BIGINT NOT NULL,
+    updated_at      BIGINT NOT NULL
+);
+CREATE INDEX idx_enhance_jobs_hash ON enhance_jobs(original_hash, created_at);
+CREATE INDEX idx_enhance_jobs_status ON enhance_jobs(status);