Field-level drift — shares/users/groups (#57)

[ChrisonSimtian]

The reconciler now does existence + field reconciliation: on an existing+desired resource it diffs field values and emits a Modify action when managed fields drift (previously existence-only).

What

• Reads current state via synoshare --get / synouser --get / synogroup --descget. New GetFields parser handles both the dotted (Comment ....[x]) and colon (User Mail : [x]) label [value] formats.
• Managed fields: share/group Description, user FullName/Email. Setters: synoshare --setdesc, synogroup --descset, synouser --modify.
  • expired is preserved (not modelled in the spec).
  • Empty/null spec fields are unmanaged — never clobbered. (So you can't blank a field via the reconciler; documented.)
  • Path changes aren't supported (that's a recreate).
• ActionKind.Modify (+ ~ modify render line showing old → new).
• 7 new reconciler tests (drift / no-drift / unmanaged / preserve-email). 19 total.

Verified live (read-only, zero mutation)

= skip   group users  (in sync)
~ modify share web  (desc 'System default shared folder' → 'DRIFT TEST - not applied')
      $ synoshare --setdesc web 'DRIFT TEST - not applied'

Still parked

List-valued fields (share ACLs, group membership) and NFS (synowebapi) — later phases.

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