Add 8 proposed changes and old trails analysis

Proposed changes (all with proposal, design, specs, tasks):
- app-navigation (9 tasks) — nav bars for both apps
- planner-landing-page (7 tasks) — standalone landing page
- planner-multiplayer-awareness (13 tasks) — participants, cursors, names
- changelog (13 tasks) — public changelog with "what's new"
- transactional-emails (15 tasks) — magic link + welcome emails
- planner-features (18 tasks) — no-go areas, notes, recovery, rate limits
- komoot-import (23 tasks) — Komoot tour import
- route-features (37 tasks) — sharing, multi-day, spatial, photos

Also adds docs/old-trails-analysis.md with feature analysis from the
older trails project.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

openspec/changes/changelog/specs/changelog/spec.md

@@ -0,0 +1,37 @@
+## ADDED Requirements
+
+### Requirement: Changelog listing page
+The system SHALL provide a public `/changelog` page showing all entries newest-first.
+
+#### Scenario: View changelog
+- **WHEN** a user visits `/changelog`
+- **THEN** all changelog entries are listed with date, title, and preview text
+
+### Requirement: Individual entry pages
+Each changelog entry SHALL have a shareable page at `/changelog/:date`.
+
+#### Scenario: View single entry
+- **WHEN** a user visits `/changelog/2026-03-25`
+- **THEN** the full markdown content of that entry is rendered
+
+#### Scenario: Social sharing meta
+- **WHEN** a changelog entry page is loaded
+- **THEN** Open Graph meta tags are set (og:title, og:description, og:url)
+
+### Requirement: Markdown file authoring
+Changelog entries SHALL be authored as markdown files with YAML frontmatter in the repository.
+
+#### Scenario: Add new entry
+- **WHEN** a developer adds a `.md` file to the changelog directory with date frontmatter
+- **THEN** it appears on the changelog page after the next deploy
+
+### Requirement: What's New indicator
+The system SHALL show a visual indicator when there are changelog entries the user hasn't seen.
+
+#### Scenario: New entry available
+- **WHEN** a user visits the app and a changelog entry is newer than their last visit to /changelog
+- **THEN** a dot or badge appears on the "Changelog" nav link
+
+#### Scenario: Indicator dismissed
+- **WHEN** a user visits the /changelog page
+- **THEN** the indicator is dismissed (localStorage timestamp updated)