feat: wire book detail page with working shelf/status moves and note posting

- Add spine-move-book: move book between shelves by cutting/pasting headline
- Add spine-set-status: change TODO keyword (WANT/READING/READ/none)
- Add action=shelf and action=status cases to httpd/edit POST handler
- Wrap shelf/status selects in forms with onchange auto-submit to /edit
- Wire note composer as POST form to /edit with action=note
- Redirect all edit POSTs back to /book?id=X
- 7 new tests for move-book and set-status (error handling, property preservation)

spine.el

@@ -390,6 +390,81 @@ Signals an error if the book is not found."
             (when (eq (point) (point-min))
               (error "spine-set-rating: no book found with ID %s" id)))
         (kill-buffer)))))
+
+(defun spine-move-book (id target-shelf)
+  "Move book with ID to TARGET-SHELF.
+The book's level-2 headline is moved under the level-1 TARGET-SHELF headline.
+Signals an error if the book or target shelf is not found."
+  (let ((org-file (expand-file-name spine-org-file))
+        (shelf-re (format "^\\*+[ \t]+%s[ \t]*$" (regexp-quote target-shelf))))
+    (unless (file-exists-p org-file)
+      (error "spine-move-book: file not found: %s" org-file))
+    (with-current-buffer (find-file-noselect org-file)
+      (unwind-protect
+          (let (book-begin book-end book-text)
+            (org-element-map (org-element-parse-buffer 'headline) 'headline
+              (lambda (hl)
+                (when (= (org-element-property :level hl) 2)
+                  (let ((hl-id (spine--prop (org-element-property :begin hl) "ID")))
+                    (when (equal id hl-id)
+                      (setq book-begin (org-element-property :begin hl))
+                      (setq book-end (org-element-property :end hl))))))
+              nil 'headline)
+            (unless book-begin
+              (error "spine-move-book: no book found with ID %s" id))
+            (setq book-text (buffer-substring-no-properties book-begin book-end))
+            (delete-region book-begin book-end)
+            ;; Re-find target shelf (positions shifted after deletion)
+            (goto-char (point-min))
+            (let ((shelf-found nil))
+              (while (and (not shelf-found)
+                          (re-search-forward shelf-re nil t))
+                (when (= (org-current-level) 1)
+                  (setq shelf-found t)))
+              (unless shelf-found
+                (error "spine-move-book: shelf \"%s\" not found" target-shelf))
+              (org-end-of-subtree)
+              (skip-chars-backward " \t\n")
+              (insert "\n")
+              (insert book-text)
+              (unless (bolp) (insert "\n"))
+              (save-buffer)
+              t))
+        (kill-buffer)))))
+
+(defun spine-set-status (id new-status)
+  "Change the TODO keyword of book with ID to NEW-STATUS.
+NEW-STATUS is one of \"want\", \"reading\", \"read\", or \"\" to remove.
+Signals an error if the book is not found."
+  (let ((org-file (expand-file-name spine-org-file))
+        (new-kw (car (rassoc new-status
+                            '(("WANT" . "want") ("READING" . "reading") ("READ" . "read"))))))
+    (unless (file-exists-p org-file)
+      (error "spine-set-status: file not found: %s" org-file))
+    (with-current-buffer (find-file-noselect org-file)
+      (unwind-protect
+          (progn
+            (org-element-map (org-element-parse-buffer 'headline) 'headline
+              (lambda (hl)
+                (when (= (org-element-property :level hl) 2)
+                  (let ((pos (org-element-property :begin hl)))
+                    (when (equal id (spine--prop pos "ID"))
+                      (goto-char pos)
+                      (let* ((raw (org-get-heading t t t t))
+                             (clean (if (string-match
+                                         "\\`\\(WANT\\|READING\\|READ\\)[ \t]+\\(.*\\)\\'"
+                                         raw)
+                                        (match-string 2 raw)
+                                      raw)))
+                        (org-edit-headline
+                         (if new-kw (format "%s %s" new-kw clean) clean)))))))
+              nil 'headline)
+            (unless (eq (point) (point-min))
+              (save-buffer)
+              t)
+            (when (eq (point) (point-min))
+              (error "spine-set-status: no book found with ID %s" id)))
+        (kill-buffer)))))
 (defun spine--extract-notes (hl-begin hl-end)
   "Extract reading notes from headline body between HL-BEGIN and HL-END.
 Returns list of (date-string text-string) pairs."
@@ -540,13 +615,13 @@ Set by test harnesses that only need the model functions.")
 
 
 (defun httpd/edit (proc uri-path query request)
-  "Handle /edit: GET shows prompt page, POST processes actions.
+  "Handle /edit: POST processes actions; GET shows prompt pages.
 Query params:
   id     - book ID
-  action - note | rating
+  action - note | rating | shelf | status
   text   - note text (for note action)
   date   - optional date string (for note action)
-  value  - rating value (for rating action)"
+  value  - rating value / shelf name / status key (for rating/shelf/status)"
   (let ((method (caar request))
         (id (cadr (assoc "id" query)))
         (action (cadr (assoc "action" query)))
@@ -559,8 +634,12 @@ Query params:
            ((equal action "note")
             (spine-add-note id text date))
            ((equal action "rating")
-            (spine-set-rating id value)))
-          (httpd-redirect proc (format "/index?id=%s" id) 303))
+            (spine-set-rating id value))
+           ((equal action "shelf")
+            (spine-move-book id value))
+           ((equal action "status")
+            (spine-set-status id value)))
+          (httpd-redirect proc (format "/book?id=%s" id) 303))
       ;; GET: show prompt page for actions needing input
       (if (and id (equal action "note"))
           (let* ((books (spine-books))