fix(copy): replace em-dashes in user-facing strings with commas/periods

Per the project's no-dashes feedback rule (see CORBEL-Main memory
feedback_no_dashes.md), em-dashes in user-visible copy are the single
biggest "AI wrote this" surface tell. Forty-two occurrences across ten
files: ten in SettingsPage's group descriptions and option labels
(audio device picker, vocabulary help, prompt placeholders, model
descriptions), four in FirstRunPage's setup steps, three in
DictationPage / FilesPage / Energy chip tooltips, plus the privacy
bullets ("100% offline, no Python required, no cloud, no accounts,
no telemetry"), the rejection toast, MicroSteps thumb labels, and the
shutdown ritual prompts.

Replacement rule: subordinate-clause em-dashes followed by lowercase
become commas; sentence-break em-dashes followed by capitals become
full stops. Code comments left intact.

One non-em-dash regression caught while reviewing: TasksPage's energy
filter "no selection" placeholder showed "—" as a literal label; the
script changed it to a comma which read as a UI bug. Replaced with
"Any" instead.

src/lib/pages/FilesPage.svelte

@@ -109,7 +109,7 @@
           modelId: result.modelId ?? null,
         });
       } catch (err) {
-        error = `Failed: ${fileName} — ${typeof err === "string" ? err : err.message}`;
+        error = `Failed: ${fileName}. ${typeof err === "string" ? err : err.message}`;
       }
     }