feat(notes): share a note with a person, not only through a project

Until now a note was shared exactly one way: file it in a shared project, and
everyone who could read the project could read the note. That is right when the
note belongs with a body of work and wrong when it is just "let Sofie see this" —
it made you stand up a project to hand over a single page.

A note can now be shared with named people directly, at viewer or editor — the
same two roles a project membership uses, so there is one idea of a role in the
program and not two. The paths stack: a note can be loose, filed, shared with
people, or any mix, and access is the most any of them allow.

The store:
  - note_shares (migration 0030): note ↔ user ↔ role, one row per person, owner
    recorded. Visibility (AllNotes, and search via mayTouchNote) widens to include
    notes shared directly with the reader.
  - the effective role folds a direct share on top of the owner and project paths.

The rules, drawn where they protect the owner:
  - read = viewer, edit text = editor, on any path.
  - MOVE a note (change its project) is owner-only: an editor filing it into a
    project the owner is not in would take the owner's own note away from them.
  - DELETE is owner or project-editor — a direct share, however high its role,
    does not reach to throwing the note away.
  - SHARE and UNSHARE are the owner's alone, like a project's invitations.
  - the picker is everyone on the instance (a closed, invited set) minus who is
    already on the note; a made-up id and the owner themselves are refused.

The list:
  - a "Delt med mig" group at the top, collapsible, that appears only when it has
    something in it — the same rule Favoritter follows — so it costs nothing when
    you share nothing. A shared note lives there, not also in a time bucket.
  - every shared note carries a small chip in its owner's avatar colour, the
    project mark's shape said for a person.
  - no star or archive button on a note somebody else owns: those change the note
    itself, and it is not yours to put away.
  - the editor grows a "Del med personer" panel for the owner: who can see it, at
    what role, and an add row drawn from the instance's other people.

The old comment in the notes footer argued against a note having an access list
of its own. That was the right call until the case it did not cover — sharing
without a project — turned out to be the one actually asked for. Updated to match.

Person now carries json tags, so a note's owner serialises as id/name/avatar_color
like every other person in the API rather than as Go field names.

Tests: a shared note reaches the other person marked and owned; a viewer reads but
cannot write; an editor writes but cannot re-share or delete; unshare removes
access and is owner-only; the candidate list excludes who is already on and the
owner; and a made-up id and self are refused. OpenAPI covers the three new routes.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

internal/store/notes.go

@@ -37,6 +37,17 @@ type Note struct {
 	// set by a caller: it is derived, and a caller that set it would be describing
 	// a note whose text says something else.
 	Links []NoteLink `json:"links,omitempty"`
+
+	// SharedWithMe is true when the person reading the list reached this note
+	// through a direct share rather than by owning it or being in its project. It
+	// is what puts the note in the Delt med mig group and shows whose note it is.
+	// Derived per request, so it is never stored and never set by a caller.
+	SharedWithMe bool `json:"shared_with_me,omitempty"`
+
+	// Owner is who the note belongs to — its created_by — as a name and a colour,
+	// for the chip on a note shared with the reader. Set only when it helps the
+	// list say something; nil the rest of the time.
+	Owner *Person `json:"owner,omitempty"`
 }
 
 // NoteLink is one reference from a note to something else.
@@ -263,8 +274,9 @@ func (db *DB) allNotes(ctx context.Context, userID string, archived bool) ([]Not
 		      UNION
 		      SELECT project_id FROM project_members WHERE user_id = ?
 		    )
+		    OR notes.id IN (SELECT note_id FROM note_shares WHERE user_id = ?)
 		  )
-		ORDER BY pinned DESC, updated_at DESC`, userID, userID, userID)
+		ORDER BY pinned DESC, updated_at DESC`, userID, userID, userID, userID)
 }
 
 // NotesLinking answers the backwards question: what points at this thing.