topdir.mk: Derive GITIGNORE_PATTERNS_END from TOP

The !-exceptions in the generated .gitignore are computed by a grep pattern
that hardcodes the project name, while the top ignore line comes from
GITIGNORE_PATTERNS_TOP. A project that overrides GITIGNORE_PATTERNS_TOP -
jw-pkg's Makefile sets it to empty - still gets the hardcoded exceptions,
and patterns a project adds there get no exceptions at all, so the two can
drift apart.

Derive the exception pattern from the same variable:

- new GITIGNORE_PATTERNS_TOP_INV joins the patterns of
  GITIGNORE_PATTERNS_TOP with |, each wrapped in word boundaries, plus the
  __init__.py pattern
- GITIGNORE_PATTERNS_END greps the tracked files for that alternation with
  grep -E instead of a hardcoded BRE, so the dot in __init__.py is literal
  instead of matching any character

With the default GITIGNORE_PATTERNS_TOP the generated .gitignore is
byte-for-byte identical to before.

Assisted-by: unsloth/Qwen3.8-27B-GGUF:Q4_K_M with pi.dev v1.0.0
Signed-off-by: Jan Lindemann <jan@janware.com>

make/topdir.mk

@@ -98,7 +98,8 @@ JW_PKG_TMPL_UPDATE          ?= $(PYTHON) $(JWB_SCRIPT_DIR)/jw-pkg.py -p $(PROJEC
 				projects create-file --format tmpl --search-path $(subst $(space),:,$(JW_PKG_TMPL_SEARCH_PATH)) --template-name
 
 GITIGNORE_PATTERNS_TOP      ?= $(PROJECT)
-GITIGNORE_PATTERNS_END      ?= $(addprefix !,$(shell git ls-files 2>/dev/null | grep "\(\b$(PROJECT)\b\|__init__.py\)" | xargs))
+GITIGNORE_PATTERNS_TOP_INV  ?= $(subst $(space),|,$(strip $(addprefix \b,$(addsuffix \b,$(GITIGNORE_PATTERNS_TOP))) __init__\.py))
+GITIGNORE_PATTERNS_END      ?= $(addprefix !,$(shell git ls-files 2>/dev/null | grep -E "($(GITIGNORE_PATTERNS_TOP_INV))" | xargs))
 
 all: topdir config
 test: all