mobile: cache-bust static assets so browser picks up CSS/JS edits

User reported phone still showing old behaviour (Qty/Avg portfolio
columns visible) even though the server-side JS had been updated.
Root cause: every <link>/<script> URL was a plain
/static/css/foo.css with no query string, so mobile Chrome served
the file from its HTTP cache rather than refetching it.

Adds a process-startup timestamp to the Jinja environment as
ASSET_VERSION (computed once when templates_env is imported). Every
<link>/<script> reference now appends `?v={{ ASSET_VERSION }}` so a
container restart bumps the URL and the browser refetches. 38 URLs
across 8 templates updated via sed; tests still pass.

Side benefit: future CSS/JS edits no longer require users to hard-
refresh.

app/templates_env.py

@@ -3,6 +3,7 @@ Imported by both routers/pages.py and routers/api.py so the filters are
 registered exactly once."""
 from __future__ import annotations
 
+import time
 from pathlib import Path
 
 from fastapi.templating import Jinja2Templates
@@ -13,6 +14,13 @@ from app.config import get_settings
 from app.services.glossary import wrap_glossary
 
 
+# Cache-busting token for static assets. Computed once at import time
+# (i.e. process startup), so every container restart yields a fresh
+# value and browsers refetch CSS/JS instead of serving stale cache.
+# Templates append `?v={{ ASSET_VERSION }}` to every static URL.
+ASSET_VERSION = str(int(time.time()))
+
+
 TEMPLATE_DIR = Path(__file__).resolve().parent / "templates"
 
 
@@ -77,3 +85,4 @@ templates.env.globals["LEGAL_OPERATOR"] = branding.LEGAL_OPERATOR
 templates.env.globals["OPERATOR_EMAIL"] = branding.OPERATOR_EMAIL
 templates.env.globals["OPERATOR_JURISDICTION"] = branding.OPERATOR_JURISDICTION
 templates.env.globals["BETA_MODE"] = get_settings().BETA_MODE
+templates.env.globals["ASSET_VERSION"] = ASSET_VERSION