feature/report sighting: multi-step wizard + smart auto-fill

[irenecancode]

Report Sighting: multi-step wizard + smart auto-fill

Summary

Refactors the single-page "Report a Sighting" form into a guided 5-step wizard (Media → Time & Place → Species → Device & Credit → Preview & Publish), and layers in EXIF-based auto-fill so users have to type less. Frontend/template-only change — no Django views, models, URLs, or migrations touched.

Wizard structure

• 5 steps behind a progress bar with Back / Next / Publish navigation; steps show/hide via CSS only (no DOM detachment), so the map, media previews, and species rows stay alive across navigation.
• Per-step required-field validation before advancing, plus a final safety-net check on Publish (native validation skips fields inside hidden ancestors, so earlier hidden steps needed their own re-check).
• Publish is only a real submit button while on the last step, so Enter in an earlier text field can't trigger an accidental early submit.

Media step

• Per-file delete button on upload previews (subtle by default, darkens on hover), backed by rebuilding the input's FileList via DataTransfer — a removed file is genuinely gone from what's submitted.
• Persistent "Media info detected" panel showing what EXIF actually found (camera, date/time, GPS), with a friendly fallback message when no location tag exists.

EXIF auto-fill (camera model, GPS, date/time)

• Fixed a real bug where Nikon-style EXIF (Make: "NIKON CORPORATION", Model: "NIKON D3500") rendered as duplicated text.
• Each auto-filled field tracks whether its value came from EXIF or the user, so removing the source photo cleanly resets it (fixing the originally reported stale-data bug), and any deliberate user action takes ownership so EXIF can never overwrite it again.
• If EXIF finds a date, the fields lock (read-only, visibly darkened) and "Use Current Date/Time" hides — a wrong camera clock is corrected via Timestamp Offset instead. No date found → fields stay blank/editable.
• Apple's Make tag auto-selects "Phone"; a localStorage-based memory (no backend field exists for this) recalls device type per camera model to cut repeat clicks.

Time & Place

• "Saved Location" / "New Location" toggle, defaulting to whichever makes sense for the account, without overriding a deliberate user choice.
• New Location supports naming + "save for next time," persisted through the existing saved-locations API.

Species

• "I'm not sure what species this is" opt-out, placed after the species rows so identification is tried first.

Device & Credit

• Device type selector (Camera/Phone/Home Camera/Trail Camera); deployment date + saved-device follow-ups only for the two installed types.
• All four device types can now save a new device (previously Home/Trail Camera only).
• Auto-recognizes an already-saved device by camera-model match and switches modes automatically; hides the redundant Camera Model field when reusing a saved device.
• Reordered to: What captured this sighting? → Device Source → Camera Model → License, with save/deployment fields after License.

Preview & Publish

• Redesigned into a feed-style card matching the site's sighting-feed look: media on top (video badge + play button for video), Title/Description edited inline, byline, location, compact meta line.
• Divider added between Public Setting/Display Name and Obfuscation Radius/Location Accuracy.
• km/m vs. mi/ft display toggle for those two fields — submitted values stay in the metric units the backend expects; only the display converts.

Explicit non-goals for this branch

• No analytics/tracking added yet. Mapped ~30 candidate tracking points (funnel drop-off, EXIF hit rate, auto-fill override rate, opt-in rates, etc.) but held off pending a decision on tooling (likely GA4 or PostHog, both free at expected volume) — planned for a follow-up branch.
• No video EXIF extraction — only image EXIF is parsed; video-only uploads fall into the "nothing detected" path.

Test plan

• Full 5-step walkthrough with a photo carrying full EXIF (camera, GPS, date/time) — confirm auto-fill + locked date/time + detection panel.
• Walkthrough with a photo lacking EXIF (e.g. screenshot) — fields stay blank/editable, fallback copy shows.
• Upload → delete → upload a different photo — confirm no stale camera/location/date data lingers.
• Toggle Saved/New Location and Device Source (New/Saved) both directions.
• Save a new location and a new device; confirm they appear as "saved" on a subsequent report.
• Submit with a Public Setting option; confirm Obfuscation Radius/Location Accuracy show/hide and unit toggle round-trips correctly.
• Confirm Expert Bulk Upload (is_expert=True) still works unaffected.
• python manage.py check + direct template render (done throughout dev; re-verify before merge).

[irenecancode]

Follow-up tracked separately: device_type is UI-only on this branch — it routes which follow-up fields show, but no backend field exists so it isn't persisted. (camera_model and camera_deployment_date do persist and are unaffected.)

Will open a backend PR to add device_type to MediaPost alongside camera_model -- Home vs. Trail Camera in particular isn't recoverable from camera_model alone. Web-side is then a one-line passthrough in sightings/views.py.

Keeping it out of this PR so the frontend work isn't blocked on a migration.

[irenecancode]

Updated privacy policy for the checkbox.