perf: round 20 — iCal/vCard parse allocs, owned-DTO moves, Result-collect pre-size, NC etag/favorites emit

Benchmark-gated (benches/ROUND20.md), same rule as rounds 2-19: every change
ships with a BEFORE/AFTER counting-allocator micro-benchmark and a byte-value
equivalence gate; a non-winning AFTER is rolled back (never applied). The
rollback rule is encoded in the harness (GATE FAIL exit). All 8 sections pass.

Reproduce: cargo run --release --features bench --example bench_round20_micro

- A1 CalendarEvent iCal parse: replace the throwaway per-property
  HashMap<String,Vec<String>> (DTSTART/DTEND/RECURRENCE-ID) with a direct
  VALUE=DATE scan; prop_with_params kept #[cfg(test)] (6->2 allocs/event, 4.2x)
- A2 UserDto::from: add User::into_parts and MOVE image (<=512 KiB data URI)
  + ui_preferences JSON instead of cloning on every /api/auth/me (27->14 allocs)
- A3 parse_vcard: drop the per-line to_ascii_uppercase copy + the lines Vec;
  promote ascii_ci_contains to common::text and share it (8->1 allocs/contact)
- A4 Calendar/AddressBook DTO: into_parts move incl. custom_properties map (18->10)
- I1 file-listing repos: collect::<Result<Vec>>() size-hints to 0 and grows from
  capacity 0; pre-size with Vec::with_capacity (8->1 container reallocs, 4 sites)
- I4 plaintext_stream: lazy emit iterator instead of eager Vec collect (43x wall)
- C1 NC write_etag_element: borrowed pre-escaped quote events, no owned quoted
  String/escape re-alloc; byte-identical output (3->0 allocs/PROPFIND row)
- C3 NC favorites REPORT: map.remove() move instead of get().clone() (~7 allocs/fav)

Deferred (documented in ROUND20.md): NC oc:id/trashbin buffer reuse, I1 sibling
CardDAV/CalDAV listing paths, Contact JSONB Json<Vec<_>> decode, dedup
settle_batch &str bind, and a fast DoS-resistant hasher for hot trusted-key maps
(needs a dependency decision).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JsJjcVX9RoN96DMa35Wqzd

src/domain/entities/calendar.rs

@@ -49,6 +49,48 @@ pub struct Calendar {
     custom_properties: std::collections::HashMap<String, String>,
 }
 
+/// Owned decomposition of a [`Calendar`] (mirrors `FileParts`/`UserParts`).
+/// Lets `CalendarDto::from` MOVE the heap fields — notably the
+/// `custom_properties` map — instead of cloning them on every CalDAV discovery
+/// listing (benches/ROUND20.md §A4).
+pub struct CalendarParts {
+    pub id: Uuid,
+    pub name: String,
+    pub owner_id: Uuid,
+    pub description: Option<String>,
+    pub color: Option<String>,
+    pub created_at: DateTime<Utc>,
+    pub updated_at: DateTime<Utc>,
+    pub custom_properties: std::collections::HashMap<String, String>,
+}
+
+impl Calendar {
+    /// Decompose into [`CalendarParts`], moving every owned field out
+    /// (exhaustive destructure — compiler-checked against added fields).
+    pub fn into_parts(self) -> CalendarParts {
+        let Calendar {
+            id,
+            name,
+            owner_id,
+            description,
+            color,
+            created_at,
+            updated_at,
+            custom_properties,
+        } = self;
+        CalendarParts {
+            id,
+            name,
+            owner_id,
+            description,
+            color,
+            created_at,
+            updated_at,
+            custom_properties,
+        }
+    }
+}
+
 impl Calendar {
     /**
      * Creates a new calendar with the given properties.