Add analytics integration with Horchposten backend

Implements session-based analytics tracking that sends gameplay
stats to the Horchposten API. Adds stats.{c,h} for accumulating
per-session metrics (kills, deaths, shots, dashes, jumps, pickups,
damage, time) and analytics.{c,h} with EM_JS bridge for fetch()
calls to the backend. Client ID is persisted in localStorage.
Session start/end hooks are wired into all game lifecycle events
(level transitions, restart, quit, tab close via sendBeacon).
Analytics URL/key are configured via data attributes on the canvas
container. Non-WASM builds compile with no-op stubs.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/main.c

@@ -4,6 +4,8 @@
 #include "game/level.h"
 #include "game/levelgen.h"
 #include "game/editor.h"
+#include "game/stats.h"
+#include "game/analytics.h"
 #include "config.h"
 #include <stdio.h>
 #include <string.h>
@@ -46,6 +48,10 @@ static int s_station_depth = 0;
 static int s_mars_depth = 0;
 #define MARS_BASE_GEN_COUNT 2
 
+/* ── Analytics / stats tracking ── */
+static GameStats s_stats;
+static bool      s_session_active = false;
+
 /* ── Pause menu state ── */
 #define PAUSE_ITEM_COUNT 3
 static int s_pause_selection = 0; /* 0=Resume, 1=Restart, 2=Quit */
@@ -238,6 +244,21 @@ static void load_mars_base_level(void) {
     s_level_path[0] = '\0';
 }
 
+/* ── Analytics session helpers ── */
+static void begin_session(void) {
+    stats_reset(&s_stats);
+    stats_set_active(&s_stats);
+    analytics_session_start();
+    s_session_active = true;
+}
+
+static void end_session(const char *reason) {
+    if (!s_session_active) return;
+    s_session_active = false;
+    stats_set_active(NULL);
+    analytics_session_end(&s_stats, reason);
+}
+
 /* ── Switch to editor mode ── */
 static void enter_editor(void) {
     if (s_mode == MODE_PLAY) {
@@ -305,15 +326,19 @@ static void restart_level(void) {
  * ═══════════════════════════════════════════════════ */
 
 static void game_init(void) {
+    analytics_init();
+
     if (s_use_editor) {
         enter_editor();
     } else if (s_use_procgen) {
         load_generated_level();
+        begin_session();
     } else {
         if (!load_level_file("assets/levels/moon01.lvl")) {
             fprintf(stderr, "Failed to load level!\n");
             g_engine.running = false;
         }
+        begin_session();
     }
 }
 
@@ -347,12 +372,15 @@ static void pause_update(void) {
             break;
         case 1: /* Restart */
             s_mode = MODE_PLAY;
+            end_session("quit");
             restart_level();
+            begin_session();
             break;
         case 2: /* Quit */
             if (s_testing_from_editor) {
                 return_to_editor();
             } else {
+                end_session("quit");
                 g_engine.running = false;
             }
             break;
@@ -364,6 +392,7 @@ static void game_update(float dt) {
     /* Handle deferred level load from JS shell dropdown. */
     if (s_js_load_request && s_js_load_path[0]) {
         s_js_load_request = 0;
+        end_session("quit");
 
         /* Tear down whatever mode we are in. */
         if (s_mode == MODE_PLAY || s_mode == MODE_PAUSED) {
@@ -389,6 +418,7 @@ static void game_update(float dt) {
         s_js_load_path[0] = '\0';
 
         SDL_SetWindowTitle(g_engine.window, "Jump 'n Run");
+        begin_session();
         return;
     }
 #endif
@@ -437,22 +467,35 @@ static void game_update(float dt) {
     bool r_pressed = input_key_held(SDL_SCANCODE_R);
     if (r_pressed && !r_was_pressed) {
         printf("\n=== Regenerating level ===\n");
+        end_session("quit");
         level_free(&s_level);
         s_gen_seed = (uint32_t)time(NULL);
         s_use_procgen = true;
         load_generated_level();
+        begin_session();
     }
     r_was_pressed = r_pressed;
 
     level_update(&s_level, dt);
 
+    /* Accumulate play time */
+    if (s_session_active) {
+        s_stats.time_elapsed += dt;
+    }
+
     /* Check for level exit transition */
     if (level_exit_triggered(&s_level)) {
         const char *target = s_level.exit_target;
 
+        /* Record the level completion in stats */
+        if (s_session_active) {
+            s_stats.levels_completed++;
+        }
+
         if (target[0] == '\0') {
             /* Empty target = victory / end of game */
             printf("Level complete! (no next level)\n");
+            end_session("completed");
             /* Loop back to the beginning, reset progression state */
             level_free(&s_level);
             s_station_depth = 0;
@@ -460,6 +503,7 @@ static void game_update(float dt) {
             if (!load_level_file("assets/levels/moon01.lvl")) {
                 g_engine.running = false;
             }
+            begin_session();
         } else if (strcmp(target, "generate") == 0) {
             /* Procedurally generated next level */
             printf("Transitioning to generated level\n");
@@ -549,6 +593,8 @@ static void game_render(float interpolation) {
 }
 
 static void game_shutdown(void) {
+    end_session("quit");
+
     /* Always free both — editor may have been initialized even if we're
      * currently in play mode (e.g. shutdown during test play). editor_free
      * and level_free are safe to call on zeroed/already-freed structs. */