docs+openspec: prior-art research (Organic Maps, Endurain, wanderer) and 15 proposals

Add docs/inspirations.md as the durable record of the 2026-07-05/06
prior-art research — per-project learnings with source paths, canonical
credit lines, and the changes each spawned — and extend the
acknowledgment lists in philosophy.md/architecture.md (Organic Maps,
Endurain, wanderer).

New OpenSpec changes (proposal/design/specs/tasks each):
- Organic Maps: elevation-profile-hardening, gpx-parser-robustness,
  hiking-time-estimate, poi-index, hiking-foot-profile
- Endurain: account-export, activity-duplicate-review,
  fit-parsing-hardening, activity-locations, self-hosting-guide,
  activity-privacy-controls
- wanderer: federation-hardening, link-share-tokens
- credits-page (user-visible acknowledgments)

Updated in-flight changes with wanderer prior-art sections:
route-federation, route-discovery.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docs/philosophy.md

@@ -37,11 +37,22 @@ trails.cool is MIT licensed. The entire codebase — Planner, Journal, shared
 packages, infrastructure — is open source.
 
 This is both a commitment to the open web and an acknowledgment of the
-projects that made trails.cool possible:
+projects that made trails.cool possible (what we learned from each is
+recorded in [docs/inspirations.md](inspirations.md); keep the two lists in
+sync):
 
 - [BRouter](https://github.com/abrensch/brouter) — the routing engine
 - [bikerouter.de](https://bikerouter.de) — inspiration for the Planner
 - [brouter-web](https://github.com/nrenner/brouter-web) — the web client
+- [Organic Maps](https://github.com/organicmaps/organicmaps) — inspiration for
+  outdoor-focused map presentation, elevation handling, hiking-time estimation
+  (Tobler), GPX robustness, and privacy-as-proof practices
+- [Endurain](https://codeberg.org/endurain-project/endurain) — inspiration for
+  the Journal's activity privacy controls, account export, duplicate handling,
+  and self-hosting operator experience
+- [wanderer](https://wanderer.to) — a self-hosted, federated trail database;
+  the closest neighbor to the Journal's federated route sharing and proof the
+  ActivityPub-for-trails idea works
 
 We benefit from open source. We contribute back to it.