feat: implement shared-album multi-user photo album

Backend (Go/Gin/pgx): env config, pgx pool with retries, Garage S3 client
(path-style, region garage), embedded golang-migrate migrations, JWT auth with
refresh rotation, albums CRUD, members/roles/invites with no-escalation matrix,
photo upload + async imaging/goexif WebP variants, cursor pagination, presigned
URLs, likes/comments, SSE hub (album + personal), notifications, share links.

Frontend (SvelteKit 2 + Svelte 5 + Tailwind v4): API wrapper with 401 refresh,
auth store, all screens, Uploader/PhotoGrid/Lightbox/Comments, SSE client with
reconnect + REST catch-up, three themes + system via data-theme.

Deploy without Docker: Makefile builds the frontend into backend/static and
embeds it (go:embed) into a single statically linked binary; systemd unit and
nginx SSE example included.

Use gen2brain/webp (-tags nodynamic) instead of cgo kolesa-team/go-webp to keep
CGO_ENABLED=0 static builds; design.md/proposal.md updated accordingly.

openspec/config.yaml

@@ -0,0 +1,32 @@
+schema: spec-driven
+
+# Project context (optional)
+# Add only constraints that should guide OpenSpec artifacts and workflows.
+# Include constraints an agent cannot infer by reading the code.
+# Keep general project documentation and discoverable codebase facts out.
+# Example:
+#   context: |
+#     Designs and tasks must cover Windows, macOS, and Linux
+#     Write all artifacts in Spanish
+
+# Per-artifact rules (optional)
+# Add custom rules for specific artifacts.
+# Example:
+#   rules:
+#     proposal:
+#       - Keep proposals under 500 words
+#       - Always state what is out of scope
+#     tasks:
+#       - Break tasks into chunks of max 2 hours
+
+# Per-operation guidance (optional)
+# Add advisory guidance for how apply and archive work should be conducted.
+# This is separate from artifact rules above.
+# Example:
+#   operations:
+#     apply:
+#       guidance:
+#         - Keep test summaries concise
+#     archive:
+#       guidance:
+#         - Summarize the archive outcome before finishing