feat: short link support

[okatu-loli]

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[Copilot]

Pull request overview

Adds first-class “share/short link” support to the server, including public share APIs, share page routing, and persistence for share metadata and access control.

Changes:

• Added /s/:share_id share page routing plus /sd (download) and /sp (proxy/preview) endpoints.
• Implemented authenticated share-management APIs (/api/share/*) and public share APIs (/api/public/share/*).
• Introduced Share model + DB migration + access-token signing and DB helpers for share access tracking.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
server/router.go	Registers share page, share download/proxy routes, and share public/private API endpoints.
server/handles/share_public.go	Implements public share info/auth/list/get plus share download/proxy handlers.
server/handles/share_page.go	Serves the SPA entry for share pages (data-page="share").
server/handles/share.go	Implements share creation/update/list/disable/delete and shared helper logic (tokens, path resolution, URL building).
internal/share/access.go	Adds HMAC-signed share access tokens with TTL and verification.
internal/model/share.go	Adds the Share GORM model and share-related helpers (expiry/consumption/access limits).
internal/db/share.go	Adds DB CRUD + counters + transactional access counting for shares.
internal/db/db.go	Adds model.Share to auto-migrations.

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