Tracing: DAO layer + handler spans on tracing, drop all Context params (#141)

trace_db_call no longer takes an OpenTelemetry Context: it opens a
db.<query_type>.<operation> span (same name via otel.name, same
db.query_type / db.operation attrs) on the caller's ambient tracing span
and runs the DAO body inside it. The cx / ctx / context parameter is gone
from every DAO trait method, impl and call site, and from the helpers and
background drains that only threaded it.

The remaining request-handler spans (files, tags, faces, image, video,
favorites, duplicates, memories) move to #[instrument]; the
Context::current_with_span / with_remote_span_context plumbing is gone, as
is extract_context_from_request (the tracing-actix-web root span covers
it). otel::set_span_attributes replaces BoxedSpan::set_attributes.

Background-job raw spans (thumbnails, video actors) are left for #142.

tests/otel_db_spans.rs pins name, attributes, status and nesting (across
an instrumented spawn); otel_traceparent now uses an #[instrument]
handler. CLAUDE.md documents the tracing conventions.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/main.rs

@@ -87,8 +87,7 @@ fn main() -> std::io::Result<()> {
     {
         use crate::database::{InsightGenerationJobDao, SqliteInsightGenerationJobDao};
         let mut dao = SqliteInsightGenerationJobDao::new();
-        let ctx = opentelemetry::Context::new();
-        match dao.recover_orphaned_jobs(&ctx) {
+        match dao.recover_orphaned_jobs() {
             Ok(n) if n > 0 => {
                 info!("Recovered {} orphaned insight generation jobs", n);
             }