build: bump FreeBSD to 15.1-RELEASE, make it override-friendly, de-version docs

- build.cfg: FREEBSD_VERSION -> ${FREEBSD_VERSION:-15.1-RELEASE}. The memstick
  URL, checksum URL, cache path, and build-manifest all derive from it, so the
  live-USB build bumps from this one line. The :- form also lets an operator
  override at build time (FREEBSD_VERSION=15.2-RELEASE ./build.sh) without
  editing git — previously a plain assignment clobbered any env value.
- docs: de-version README/BUILD/REQUIREMENTS + iso-build skill from '15.0' to
  '15.x' so they stop drifting on every point release.

Verified: default derives the 15.1 memstick URL (HTTP 200, dated 12.jun.2026);
env override cascades to 15.2. ABI stays FreeBSD:15:amd64 (same major — no
package rebuild needed). build-vps.sh (mfsbsd) and poudriere keep their own
version knobs and are intentionally untouched (ABI-compatible, separate paths).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

BUILD.md

@@ -1,6 +1,6 @@
 # Clawdie ISO Builder
 
-On `xfce-operator-usb`, builds a bootable FreeBSD 15.0 operator USB image with:
+On `xfce-operator-usb`, builds a bootable FreeBSD 15.x operator USB image with:
 
 - XFCE desktop
 - pre-SDDM live GPU detection
@@ -41,7 +41,7 @@ sudo pkg install -y curl node24 npm-node24 sudo
 
 Also required:
 
-- FreeBSD 15.0+
+- FreeBSD 15.x
 - 150 GB free build space recommended
 - root or `sudo` for image assembly
 - 32 GB USB key minimum for the current default `IMAGE_SIZE=28G`
@@ -400,7 +400,7 @@ The build header shows:
 
 ```text
 ISO     : <iso-version>-dev
-FreeBSD : 15.0-RELEASE amd64
+FreeBSD : 15.x-RELEASE amd64
 Clawdie : main
 Clawdie commit: <resolved-sha>
 ```

README.md

@@ -28,7 +28,7 @@ bundled Clawdie-AI from `main`. Public release images should use
 
 Boot a USB and land in an operator environment:
 
-- FreeBSD 15.0 base system
+- FreeBSD 15.x base system
 - XFCE desktop via SDDM interactive login
 - pre-SDDM live GPU detection for Intel, AMD/ATI, VMware, and NVIDIA auto-detection with a universal driver lane
 - Firefox browser on the live image
@@ -103,7 +103,7 @@ session wrapper, but docs should teach `clawdie-gui` as the stable command.
 
 Build host:
 
-- FreeBSD 15.0+
+- FreeBSD 15.x
 - `pkg`, `curl`, Node/npm, `sudo`
 - root or `sudo` for image assembly (`mdconfig`, mount, bootcode)
 - 150 GB free build space recommended
@@ -158,7 +158,7 @@ The build prints provenance similar to:
 
 ```text
 ISO     : <iso-version>-dev
-FreeBSD : 15.0-RELEASE amd64
+FreeBSD : 15.x-RELEASE amd64
 Clawdie : main
 Clawdie commit: <sha>
 ```

REQUIREMENTS.md

@@ -8,7 +8,7 @@ Build and test requirements for the current unified Clawdie operator USB branch.
 
 Before building:
 
-- [ ] FreeBSD 15.0+ build host
+- [ ] FreeBSD 15.x build host
 - [ ] 150 GB free build space recommended
 - [ ] 32 GB USB key minimum (`IMAGE_SIZE=28G`)
 - [ ] Internet access for fetch phase
@@ -25,7 +25,7 @@ Before booting/testing:
 
 ### Operating System
 
-- FreeBSD 15.0+
+- FreeBSD 15.x
 - ZFS recommended for comfortable build storage, but not required by `build.sh`
 
 ### Packages

build.cfg

@@ -2,7 +2,7 @@
 # clawdie-iso build configuration
 # Sourced by build.sh — edit before building
 
-FREEBSD_VERSION="15.0-RELEASE"
+FREEBSD_VERSION="${FREEBSD_VERSION:-15.1-RELEASE}"
 FREEBSD_ARCH="amd64"
 FREEBSD_RELEASE_SERIES="${FREEBSD_VERSION%-RELEASE}"
 FREEBSD_ISO_BASE_URL="https://download.freebsd.org/releases/${FREEBSD_ARCH}/${FREEBSD_ARCH}/ISO-IMAGES/${FREEBSD_RELEASE_SERIES}"

skills/iso-build/SKILL.md

@@ -316,8 +316,8 @@ Mounted-image checks should confirm:
 
 If you plan another rebuild soon, keep:
 
-- `tmp/cache/FreeBSD-15.0-RELEASE-amd64-memstick.img`
+- `tmp/cache/FreeBSD-15.x-RELEASE-amd64-memstick.img`
-- `tmp/cache/FreeBSD-15.0-RELEASE-amd64-memstick.img.SHA256`
+- `tmp/cache/FreeBSD-15.x-RELEASE-amd64-memstick.img.SHA256`
 - `tmp/packages/`
 - `tmp/npm-globals/`