feat(ecosystem): compliant Praxis/Hexis integration + vendored build

Bring the Nexus/Praxis/Hexis integration in line with
MAVEN_ECOSYSTEM_ARCHITECTURE.md:

- Praxis over HTTP: drop the in-process praxis.db open (praxisstore/
  praxistools) and call praxisd's /api/v1/tools/* API via a new praxisClient.
  Honors the "no component reads another's DB" invariant (AC#12).
  PraxisConfig.DBPath -> URL.
- Hexis confirmation gate: mutating capabilities (ReadOnly=false) now park a
  bound pendingHexis confirmation and require a spoken "да" before executing;
  read-only run immediately (AC#7, no auto attention->action).
- Capability safety: >1 verb match is ambiguous -> ask instead of firing the
  first; ambiguous Nexus resolution asks for clarification (AC#2).
- Correlation IDs on Hexis execute, recorded in the cross-service trace.
- Bug: importance arrives as JSON float64 over HTTP, not int.
- Tests: confirm-gate, decline, read-only, and ambiguity paths.

Build: vendor/ bakes in the hexis client (replace-directed at a sibling repo
outside the Docker context); Dockerfile builds from vendor and no longer
`go mod download`s the unreachable replace paths.

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

vendor/github.com/google/uuid/hash.go

@@ -0,0 +1,59 @@
+// Copyright 2016 Google Inc.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package uuid
+
+import (
+	"crypto/md5"
+	"crypto/sha1"
+	"hash"
+)
+
+// Well known namespace IDs and UUIDs
+var (
+	NameSpaceDNS  = Must(Parse("6ba7b810-9dad-11d1-80b4-00c04fd430c8"))
+	NameSpaceURL  = Must(Parse("6ba7b811-9dad-11d1-80b4-00c04fd430c8"))
+	NameSpaceOID  = Must(Parse("6ba7b812-9dad-11d1-80b4-00c04fd430c8"))
+	NameSpaceX500 = Must(Parse("6ba7b814-9dad-11d1-80b4-00c04fd430c8"))
+	Nil           UUID // empty UUID, all zeros
+
+	// The Max UUID is special form of UUID that is specified to have all 128 bits set to 1.
+	Max = UUID{
+		0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
+		0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
+	}
+)
+
+// NewHash returns a new UUID derived from the hash of space concatenated with
+// data generated by h.  The hash should be at least 16 byte in length.  The
+// first 16 bytes of the hash are used to form the UUID.  The version of the
+// UUID will be the lower 4 bits of version.  NewHash is used to implement
+// NewMD5 and NewSHA1.
+func NewHash(h hash.Hash, space UUID, data []byte, version int) UUID {
+	h.Reset()
+	h.Write(space[:]) //nolint:errcheck
+	h.Write(data)     //nolint:errcheck
+	s := h.Sum(nil)
+	var uuid UUID
+	copy(uuid[:], s)
+	uuid[6] = (uuid[6] & 0x0f) | uint8((version&0xf)<<4)
+	uuid[8] = (uuid[8] & 0x3f) | 0x80 // RFC 4122 variant
+	return uuid
+}
+
+// NewMD5 returns a new MD5 (Version 3) UUID based on the
+// supplied name space and data.  It is the same as calling:
+//
+//  NewHash(md5.New(), space, data, 3)
+func NewMD5(space UUID, data []byte) UUID {
+	return NewHash(md5.New(), space, data, 3)
+}
+
+// NewSHA1 returns a new SHA1 (Version 5) UUID based on the
+// supplied name space and data.  It is the same as calling:
+//
+//  NewHash(sha1.New(), space, data, 5)
+func NewSHA1(space UUID, data []byte) UUID {
+	return NewHash(sha1.New(), space, data, 5)
+}