docs: point directory links at their folder's README

Bare-folder links (e.g. docs/postmortems/) only resolve on GitHub's
auto-render; retarget them to the folder's README.md so they open a
real file in any markdown viewer.

README.md

@@ -9,7 +9,7 @@ runs on it.
 > in spikes. No release has shipped yet — v0.1 is blocked on SD (waiting on a
 > compatible card), the boot splash, and wiring the save/publish path into the
 > app binary. Live per-item status: [`docs/roadmap.md`](docs/roadmap.md) ·
-> failure write-ups: [`docs/postmortems/`](docs/postmortems/).
+> failure write-ups: [`docs/postmortems/`](docs/postmortems/README.md).
 
 ---
 
@@ -147,6 +147,6 @@ package.json              pnpm + oxfmt — formatting toolchain for docs/JSON
 Retired risks ([gix push](docs/postmortems/2026-07-05-spike7-gix-https-push.md),
 TinyUSB HID stability, TLS heap, libgit2-on-xtensa) and how they died:
 [`docs/spikes.md`](docs/spikes.md) and
-[`docs/postmortems/`](docs/postmortems/).
+[`docs/postmortems/`](docs/postmortems/README.md).
 
 These get resolved by writing code, not by deciding harder.

docs/adr.md

@@ -234,7 +234,7 @@ over `file://` and `ssh://` — **not HTTP(S)** — so with HTTPS + PAT fixed by
 [ADR-005], the smart-HTTP push path this ADR bet on does not exist yet. We
 switched to **`libgit2` (`git2` crate)** and proved `add → commit → push`
 (incl. `pull --no-edit` + retry) on desktop
-([`spikes/spike7-git-push`](../spikes/spike7-git-push/)). The remaining risk is
+([`spikes/spike7-git-push`](../spikes/spike7-git-push/README.md)). The remaining risk is
 now the on-device **libgit2 → xtensa/mbedtls cross-compile** — the very pain
 this ADR chose gix to avoid. Full context:
 [postmortem](postmortems/2026-07-05-spike7-gix-https-push.md). Revisit gix if

docs/hardware.md

@@ -28,7 +28,7 @@ rewrite.
 The board is on the bench and bring-up is largely done — per-spike results
 live in [`spikes.md`](spikes.md) and
 [`v0.1-mvp-technical.md`](v0.1-mvp-technical.md#hardware-bring-up-order),
-with failure write-ups in [`postmortems/`](postmortems/). Notable: the
+with failure write-ups in [`postmortems/`](postmortems/README.md). Notable: the
 keyboard runs bus-powered on the S3's native USB port, and SD wiring is
 proven on shared SPI2 but blocked on a compatible ≤32 GB card
 ([postmortem](postmortems/2026-07-05-spike3-sd-cmd59.md)).

docs/postmortems/2026-07-05-spike7-gix-https-push.md

@@ -10,7 +10,7 @@
 > [`../v0.1-mvp-technical.md`](../v0.1-mvp-technical.md#hardware-bring-up-order),
 > git impl [ADR-004](../adr.md#adr-004-git-implementation--gitoxide-gix), auth
 > [ADR-005](../adr.md#adr-005-auth--https--github-personal-access-token).
-> Spike program: [`../../spikes/spike7-git-push/`](../../spikes/spike7-git-push/).
+> Spike program: [`../../spikes/spike7-git-push/`](../../spikes/spike7-git-push/README.md).
 
 ## Summary
 
@@ -34,7 +34,7 @@ is met at the library level.
 **Decision:** take the fallback the risk table already names — `libgit2` via the
 [`git2`](https://docs.rs/git2) crate — keeping ADR-005 (HTTPS + PAT) intact.
 Proved the full `add → commit → push` sequence on desktop
-([`spikes/spike7-git-push`](../../spikes/spike7-git-push/)).
+([`spikes/spike7-git-push`](../../spikes/spike7-git-push/README.md)).
 
 ## Why not the alternatives