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/dustin/go-humanize/ftoa.go

@@ -0,0 +1,49 @@
+package humanize
+
+import (
+	"strconv"
+	"strings"
+)
+
+func stripTrailingZeros(s string) string {
+	if !strings.ContainsRune(s, '.') {
+		return s
+	}
+	offset := len(s) - 1
+	for offset > 0 {
+		if s[offset] == '.' {
+			offset--
+			break
+		}
+		if s[offset] != '0' {
+			break
+		}
+		offset--
+	}
+	return s[:offset+1]
+}
+
+func stripTrailingDigits(s string, digits int) string {
+	if i := strings.Index(s, "."); i >= 0 {
+		if digits <= 0 {
+			return s[:i]
+		}
+		i++
+		if i+digits >= len(s) {
+			return s
+		}
+		return s[:i+digits]
+	}
+	return s
+}
+
+// Ftoa converts a float to a string with no trailing zeros.
+func Ftoa(num float64) string {
+	return stripTrailingZeros(strconv.FormatFloat(num, 'f', 6, 64))
+}
+
+// FtoaWithDigits converts a float to a string but limits the resulting string
+// to the given number of decimal places, and no trailing zeros.
+func FtoaWithDigits(num float64, digits int) string {
+	return stripTrailingZeros(stripTrailingDigits(strconv.FormatFloat(num, 'f', 6, 64), digits))
+}