v1.3.0

Add traffic-source segmentation to results (v1.3.0)

Capture first-touch traffic source (channel, source/medium, campaign,
referrer host, device) on each new sticky assignment, then break down
experiment results by it on the dashboard so a variant's hidden win or
loss inside one audience becomes visible.

Attribution lives at the assignment grain: source is detected once, when
the sticky row is created (before any redirect variant fires), and every
later event the visitor records inherits it via a join, so an off-target
thank-you-page conversion still attributes to the channel the visitor
first arrived through.

- New PBD_Exp_Traffic_Source classifier (GA-style, filterable rules)
- Six source columns on the assignments table, DB_VERSION 1.3.0
- Allowlist-guarded grouped repo queries for visitors/conversions
- Dashboard "Break down by traffic source" card with Channel / Source /
  Medium / Device tabs, low-sample dimming, and a diagnostic caution
- Channel + Device breakdowns frozen into the conclusion snapshot;
  archive renders them read-only and stays backward-compatible with
  pre-feature snapshots

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

v1.2.1

Add per-experiment "Reset stats" action (v1.2.1)

Clears a single experiment's collected data back to zero without touching
its configuration, for wiping QA traffic before a real run. A "Reset stats"
button in the editor status bar (shown for active and paused experiments)
deletes that experiment's rows from the events and assignments tables, so
every dashboard count returns to zero while variants, metrics, and settings
are kept. Concluded experiments are refused server-side: their frozen
snapshot is the historical record, so clone to re-run instead.

- Repo: reset_stats() deletes events + assignments for one experiment,
  returns the removed counts. Snapshots are left alone.
- Edit: handle_reset_stats() guards on manage_options + nonce (via the
  shared post router) and blocks concluded experiments; new status-bar
  button with a confirm dialog; stats_reset / reset_locked flash notices.
- Admin: route the reset_stats post action.
- Version bumped to 1.2.1 in the header and PBD_EXP_VERSION. No schema
  change, so DB_VERSION stays 1.2.0.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

v1.2.0

Add selector-driven form conversion triggers and surface unattributed…