fix: share-residence import preview polish (closes gitea#7)

Issue #7 called out four problems with the QuickLook preview iOS
recipients see when they open a `.honeydue` invite (e.g. via AirDrop or
Save to Files). All four fixed here.

1. Filename: keep spaces and apostrophes
   `HoneyDueShareCodec.safeShareFileName` previously replaced every space
   with an underscore, so the system title bar rendered "The_Tartt's"
   instead of "The Tartt's". Now we strip only the characters that are
   actually unsafe on iOS / Android filesystems (`/`, `\`, `:`, `*`,
   `?`, `"`, `<`, `>`, `|`, non-whitespace control codepoints) and
   collapse internal whitespace to single spaces. Locked in with six
   new commonTest cases.

2. Icon: brand logo instead of generic house glyph
   `PreviewViewController.updateUIForResidence` was using
   `UIImage(systemName: "house.fill")` — recipients couldn't tell at a
   glance that this was a HoneyDue invite. The honeyDue app logo
   (Assets.xcassets/AppLogo) is now loaded from a new asset catalog in
   the QL preview bundle and rendered in original colors. SF Symbol
   fallback retained for any asset-load failure.

3. Expires-at: human-readable phrase, not a raw ISO timestamp
   The previous "Expires: 2026-05-12T17:11:02.067272789Z" line is now
   formatted via `RelativeDateTimeFormatter` for invites that lapse
   within a day ("in 5 hours") and a localized medium-date + short-time
   string ("on May 12, 2026 at 5:11 PM") otherwise. Already-expired
   links render "expired 2 hours ago". Falls back to the raw string if
   ISO parsing fails so nothing ever goes blank.

4. Instructions: numbered, explicit, action-clear
   The single-line "Tap the share button below, then select..." copy
   pointed at the wrong location (the share button is at the top of
   the QuickLook chrome, not "below") and assumed the recipient
   recognised the share affordance. Replaced with a three-step list.

Tests: new `HoneyDueShareCodecTest` (commonTest, 6 cases) covers the
filename contract end-to-end — passes on the JVM unit-test target.
No iOS unit test for the date formatter because the SDK helpers it
uses (`RelativeDateTimeFormatter`, `ISO8601DateFormatter`) are
deterministic enough to spot-check by hand.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

composeApp/src/commonMain/kotlin/com/tt/honeyDue/models/HoneyDueShareCodec.kt

@@ -59,12 +59,29 @@ object HoneyDueShareCodec {
 
     /**
      * Build a filesystem-safe package filename with `.honeydue` extension.
+     *
+     * Strips only the characters that are actually unsafe on iOS / Android
+     * filesystems (`/`, `\`, `:`, `*`, `?`, `"`, `<`, `>`, `|`, control
+     * chars). Spaces and apostrophes are kept intact so the recipient sees
+     * the original residence / contractor name in the iOS QuickLook title
+     * bar — gitea#7 called out the previous behaviour rendering
+     * "The_Tartt's" instead of "The Tartt's". Internal whitespace is
+     * collapsed to single spaces and trimmed; falls back to "honeyDue" if
+     * the input is blank after sanitising.
      */
     fun safeShareFileName(displayName: String): String {
         val safeName = displayName
-            .replace(" ", "_")
-            .replace("/", "-")
+            // Keep whitespace through the filter so adjacent space+tab
+            // sequences survive to the regex-collapse step below. Drop
+            // only non-whitespace control chars (NUL etc.) plus the
+            // explicit filesystem-unsafe set.
+            .filter { it !in UNSAFE_FILENAME_CHARS && (it.isWhitespace() || !it.isISOControl()) }
+            .replace(Regex("\\s+"), " ")
+            .trim()
             .take(50)
+            .ifBlank { "honeyDue" }
         return "$safeName.honeydue"
     }
+
+    private val UNSAFE_FILENAME_CHARS = setOf('/', '\\', ':', '*', '?', '"', '<', '>', '|')
 }