refactor(store): single account name on users; rename profile/laps tables

users.display_name becomes users.name and is now the only human-facing
name -- profiles.name is dropped (it duplicated the account name; the
Profile page's Name field now edits users.name through PUT /api/profile,
which carries Name alongside the profiles columns). The profile table
becomes profiles and laps becomes activity_laps, homogeneous with
activity_samples. Onboarding pre-fills the display name from the OIDC
claim's name.

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

docs/DATABASE.md

@@ -5,11 +5,11 @@ Generated from the live schema via `go run ./cmd/dumpschema` -- do not hand-edit
 ## Tables
 
 - [`users`](#users)
-- [`profile`](#profile)
+- [`profiles`](#profiles)
 - [`workout_kinds`](#workout_kinds)
 - [`workout_type_paces`](#workout_type_paces)
 - [`activities`](#activities)
-- [`laps`](#laps)
+- [`activity_laps`](#activity_laps)
 - [`activity_samples`](#activity_samples)
 - [`kind_assignments`](#kind_assignments)
 - [`sync_state`](#sync_state)
@@ -20,20 +20,19 @@ Generated from the live schema via `go run ./cmd/dumpschema` -- do not hand-edit
 
 ```sql
 CREATE TABLE users (
-    id           INTEGER PRIMARY KEY AUTOINCREMENT,
-    oidc_sub     TEXT NOT NULL UNIQUE,
-    display_name TEXT NOT NULL,
-    created_at   TEXT NOT NULL DEFAULT (datetime('now'))
+    id         INTEGER PRIMARY KEY AUTOINCREMENT,
+    oidc_sub   TEXT NOT NULL UNIQUE,
+    name       TEXT NOT NULL,
+    created_at TEXT NOT NULL DEFAULT (datetime('now'))
 );
 ```
 
-## `profile`
+## `profiles`
 
 ```sql
-CREATE TABLE profile (
+CREATE TABLE profiles (
     id                  INTEGER PRIMARY KEY AUTOINCREMENT,
     user_id             INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
-    name                TEXT NOT NULL DEFAULT 'Default',
     garmin_email        TEXT NOT NULL DEFAULT '',
     garmin_password     TEXT NOT NULL DEFAULT '',
     -- Set once, the first time this user successfully authenticates with
@@ -171,10 +170,10 @@ Indexes:
 CREATE INDEX idx_activities_start_time ON activities(start_time_utc);
 ```
 
-## `laps`
+## `activity_laps`
 
 ```sql
-CREATE TABLE laps (
+CREATE TABLE activity_laps (
     id                      INTEGER PRIMARY KEY AUTOINCREMENT,
     activity_id             INTEGER NOT NULL REFERENCES activities(id) ON DELETE CASCADE,
     lap_index               INTEGER NOT NULL,